diff --git a/includes/Admin.php b/includes/Admin.php
index 82a3c628e..3da32d8b2 100644
--- a/includes/Admin.php
+++ b/includes/Admin.php
@@ -1,6 +1,11 @@
 <?php
 
-function commonsbooking_admin() {
+/**
+ * Enqueue scripts and styles for admin pages.
+ *
+ * @return void
+ */
+function commonsbooking_admin(): void {
 	// jQuery
 	wp_enqueue_script( 'jquery' );
 
@@ -213,14 +218,14 @@ function commonsbooking_sanitizeHTML( $string ): string {
 /**
  * Create filter hooks for cmb2 fields
  *
- * @param array $field_args  Array of field args.
+ * @param array<string, mixed> $field_args  Array of field args.
  *
  *
  * : https://cmb2.io/docs/field-parameters#-default_cb
  *
  * @return mixed
  */
-function commonsbooking_filter_from_cmb2( $field_args ) {
+function commonsbooking_filter_from_cmb2( array $field_args ) {
 	// Only return default value if we don't have a post ID (in the 'post' query variable)
 	if ( isset( $_GET['post'] ) ) {
 		// No default value.
@@ -260,14 +265,14 @@ function cmb2_set_checkbox_default_for_new_post() {
 /**
  * Recursive sanitation for text or array
  *
- * @param array|string $data
+ * @param array<mixed>|string $data
  * @param string       $sanitizeFunction name of the sanitziation function, default = sanitize_text_field. You can use any method that accepts a string as parameter
  *
  *       See more wordpress sanitization functions: https://developer.wordpress.org/themes/theme-security/data-sanitization-escaping/
  *
- * @return array|string
+ * @return array<mixed>|string
  */
-function commonsbooking_sanitizeArrayorString( $data, $sanitizeFunction = 'sanitize_text_field' ) {
+function commonsbooking_sanitizeArrayorString( array|string $data, string $sanitizeFunction = 'sanitize_text_field' ): array|string {
 	if ( is_array( $data ) ) {
 		foreach ( $data as $key => $value ) {
 			$data[ $key ] = commonsbooking_sanitizeArrayorString( $value, $sanitizeFunction );
diff --git a/includes/Public.php b/includes/Public.php
index 196680c54..63a0fd9e8 100644
--- a/includes/Public.php
+++ b/includes/Public.php
@@ -7,7 +7,12 @@
 use CommonsBooking\View\View;
 
 
-function commonsbooking_public() {
+/**
+ * Enqueue scripts and styles for public-facing pages.
+ *
+ * @return void
+ */
+function commonsbooking_public(): void {
 
 	wp_enqueue_style(
 		'cb-styles-public',
@@ -143,8 +148,13 @@ function commonsbooking_public() {
 add_action( 'wp_ajax_cb_map_geo_search', array( MapData::class, 'geo_search' ) );
 add_action( 'wp_ajax_nopriv_cb_map_geo_search', array( MapData::class, 'geo_search' ) );
 
-// Query vars
-function commonsbooking_query_vars( $qvars ) {
+/**
+ * Register custom query vars for CommonsBooking.
+ *
+ * @param string[] $qvars Existing query vars.
+ * @return string[]
+ */
+function commonsbooking_query_vars( array $qvars ): array {
 	$qvars[] = 'cb-location';
 	$qvars[] = 'cb-item';
 	$qvars[] = 'cb-type';
diff --git a/includes/Shortcodes.php b/includes/Shortcodes.php
index a4a750439..22b094c26 100644
--- a/includes/Shortcodes.php
+++ b/includes/Shortcodes.php
@@ -1,6 +1,12 @@
 <?php
 
-function commonsbooking_tag( $atts ) {
+/**
+ * Shortcode handler for [cb] shortcode.
+ *
+ * @param array<string, string>|string $atts Shortcode attributes.
+ * @return string
+ */
+function commonsbooking_tag( array|string $atts ): string {
 	$atts = shortcode_atts(
 		array(
 			'tag' => '',
@@ -9,7 +15,7 @@ function commonsbooking_tag( $atts ) {
 		'cb'
 	);
 
-	echo commonsbooking_sanitizeHTML( commonsbooking_parse_shortcode( $atts['tag'] ) );
+	return commonsbooking_sanitizeHTML( commonsbooking_parse_shortcode( $atts['tag'] ) );
 }
 
 add_shortcode( 'cb', 'commonsbooking_tag' );
diff --git a/includes/TemplateParser.php b/includes/TemplateParser.php
index 9e52a4a22..1470f6811 100644
--- a/includes/TemplateParser.php
+++ b/includes/TemplateParser.php
@@ -6,12 +6,12 @@
  * Parses templates and extracts the template tags used in e-mail templates: {{xxx:yyyy}}
  *
  * @param string   $template
- * @param array    $objects
+ * @param array<string, mixed> $objects
  * @param callable $sanitizeFunction The callable used to remove unwanted tags/characters (use default 'commonsbooking_sanitizeHTML' or 'sanitize_text_field')
  *
  * @return mixed
  */
-function commonsbooking_parse_template( string $template = '', $objects = [], $sanitizeFunction = 'commonsbooking_sanitizeHTML' ) {
+function commonsbooking_parse_template( string $template = '', array $objects = [], $sanitizeFunction = 'commonsbooking_sanitizeHTML' ) {
 	$template = preg_replace_callback(
 		'/\{{.*?\}}/',
 		function ( $match ) use ( $objects, $sanitizeFunction ) {
@@ -40,7 +40,13 @@ function ( $match ) use ( $objects, $sanitizeFunction ) {
 	}
 }
 
-function commonsbooking_parse_shortcode( $tag ) {
+/**
+ * Parses a single shortcode tag.
+ *
+ * @param string $tag
+ * @return mixed
+ */
+function commonsbooking_parse_shortcode( string $tag ) {
 	$tag = (array) $tag;
 	return commonsbooking_parse_template_callback( $tag );
 }
@@ -52,7 +58,7 @@ function commonsbooking_parse_shortcode( $tag ) {
  * Example: {{[this comes before: ]item:post_title[this comes after]}}
  *
  * @param mixed    $match
- * @param array    $objects
+ * @param array<string, mixed> $objects
  * @param callable $sanitizeFunction The callable used to remove unwanted tags/characters
  *
  * @return false|mixed
diff --git a/includes/Users.php b/includes/Users.php
index c3220544b..4f42448dd 100644
--- a/includes/Users.php
+++ b/includes/Users.php
@@ -7,12 +7,12 @@
 /**
  * Checks if current user is allowed to edit custom post.
  *
- * @param $post
+ * @param \WP_Post|int $post
  *
  * @return bool
  * @throws Exception
  */
-function commonsbooking_isCurrentUserAllowedToEdit( $post ): bool {
+function commonsbooking_isCurrentUserAllowedToEdit( \WP_Post|int $post ): bool {
 	if ( ! is_user_logged_in() ) {
 		return false; }
 
@@ -24,13 +24,13 @@ function commonsbooking_isCurrentUserAllowedToEdit( $post ): bool {
 /**
  * Checks if user is allowed to edit custom post.
  *
- * @param $post
- * @param $user
+ * @param \WP_Post|int $post
+ * @param WP_User $user
  *
  * @return bool
  * @throws Exception
  */
-function commonsbooking_isUserAllowedToEdit( $post, WP_User $user ): bool {
+function commonsbooking_isUserAllowedToEdit( \WP_Post|int $post, WP_User $user ): bool {
 
 	if ( ! Plugin::isPostCustomPostType( $post ) ) {
 		return false;
@@ -52,9 +52,10 @@ function commonsbooking_isUserAllowedToEdit( $post, WP_User $user ): bool {
 /**
  * Validates if current user is allowed to edit current post in admin.
  *
- * @param $current_screen
+ * @param \WP_Screen $current_screen
+ * @return void
  */
-function commonsbooking_validate_user_on_edit( $current_screen ) {
+function commonsbooking_validate_user_on_edit( \WP_Screen $current_screen ): void {
 	if ( $current_screen->base == 'post' && in_array( $current_screen->id, Plugin::getCustomPostTypesLabels() ) ) {
 		if ( array_key_exists( 'action', $_GET ) && $_GET['action'] == 'edit' ) {
 			$post = get_post( intval( $_GET['post'] ) );
@@ -127,14 +128,25 @@ function ( $posts, $query ) {
 	add_filter( 'views_edit-' . $custom_post_type, 'commonsbooking_custom_view_count', 10, 1 );
 }
 
-// Filter function for fix of counts in admin lists for custom post types.
-function commonsbooking_custom_view_count( $views ) {
+/**
+ * Filter function for fix of counts in admin lists for custom post types.
+ *
+ * @param array<string, string> $views
+ * @return array<string, string>
+ */
+function commonsbooking_custom_view_count( array $views ): array {
 	global $current_screen;
 	return commonsbooking_fix_view_counts( str_replace( 'edit-', '', $current_screen->id ), $views );
 }
 
-// fixes counts for custom posts countings in admin list
-function commonsbooking_fix_view_counts( $postType, $views ) {
+/**
+ * Fixes counts for custom posts countings in admin list.
+ *
+ * @param string $postType
+ * @param array<string, string> $views
+ * @return array<string, string>
+ */
+function commonsbooking_fix_view_counts( string $postType, array $views ): array {
 	// admin is allowed to see all posts
 	if ( commonsbooking_isCurrentUserAdmin() ) {
 		return $views;
@@ -165,8 +177,12 @@ function commonsbooking_fix_view_counts( $postType, $views ) {
 	return array_intersect_key( $views, $counts );
 }
 
-// Check if current user has admin role
-function commonsbooking_isCurrentUserAdmin() {
+/**
+ * Check if current user has admin role.
+ *
+ * @return bool
+ */
+function commonsbooking_isCurrentUserAdmin(): bool {
 	if ( ! is_user_logged_in() ) {
 		return false; }
 	$user = wp_get_current_user();
@@ -225,8 +241,12 @@ function commonsbooking_isUserCBManager( \WP_User $user ): bool {
 	return apply_filters( 'commonsbooking_isCurrentUserCBManager', $isManager, $user );
 }
 
-// Check if current user has subscriber role
-function commonsbooking_isCurrentUserSubscriber() {
+/**
+ * Check if current user has subscriber role.
+ *
+ * @return bool
+ */
+function commonsbooking_isCurrentUserSubscriber(): bool {
 	$user = wp_get_current_user();
 
 	$isSubscriber = in_array( 'subscriber', $user->roles );
@@ -340,12 +360,12 @@ function commonsbooking_isUserAllowedToSee( $post, WP_User $user ): bool {
  *
  * Used by Service\iCalendar for authentication.
  *
- * @param $user_id
- * @param $user_hash
+ * @param int|string $user_id
+ * @param string $user_hash
  *
  * @return bool
  */
-function commonsbooking_isUIDHashComboCorrect( $user_id, $user_hash ): bool {
+function commonsbooking_isUIDHashComboCorrect( int|string $user_id, string $user_hash ): bool {
 	if ( wp_hash( $user_id ) == $user_hash ) {
 		return true;
 	} else {
diff --git a/phpstan.neon b/phpstan.neon
index 913034c5c..863cae154 100644
--- a/phpstan.neon
+++ b/phpstan.neon
@@ -13,7 +13,7 @@ parameters:
     - commonsbooking.php
     - src/
     - includes/
-  level: 5
+  level: 6
   ignoreErrors:
     - '#Constant (COMMONSBOOKING.*|WP_DEBUG_LOG) not found.#'
 #    - '#Instantiated class (CommonsBooking.*CB_Data) not found.#'
diff --git a/src/API/AvailabilityRoute.php b/src/API/AvailabilityRoute.php
index 026256be6..9df470a01 100644
--- a/src/API/AvailabilityRoute.php
+++ b/src/API/AvailabilityRoute.php
@@ -38,9 +38,9 @@ class AvailabilityRoute extends BaseRoute {
 	/**
 	 * This retrieves bookable timeframes and the different items assigned, with their respective availability.
 	 *
-	 * @param bool $id The id of a {@see \CommonsBooking\Wordpress\CustomPostType\Item::post_type} post to search for
+	 * @param bool|int $id The id of a {@see \CommonsBooking\Wordpress\CustomPostType\Item::post_type} post to search for
 	 *
-	 * @return array
+	 * @return array<int, mixed>
 	 * @throws Exception
 	 */
 	public function getItemData( $id = false ): array {
@@ -57,11 +57,11 @@ public function getItemData( $id = false ): array {
 	/**
 	 * Get one item from the collection
 	 *
-	 * @param $request WP_REST_Request
+	 * @param WP_REST_Request<array<string, mixed>> $request
 	 *
 	 * @return WP_REST_Response|WP_Error
 	 */
-	public function get_item( $request ) {
+	public function get_item( WP_REST_Request $request ) {
 		// get parameters from request
 		$params = $request->get_params();
 		$data   = new stdClass();
@@ -76,11 +76,11 @@ public function get_item( $request ) {
 	/**
 	 * Get a collection of items
 	 *
-	 * @param $request WP_REST_Request full data about the request.
+	 * @param WP_REST_Request<array<string, mixed>> $request Full data about the request.
 	 *
 	 * @return WP_REST_Response
 	 */
-	public function get_items( $request ) {
+	public function get_items( WP_REST_Request $request ) {
 		$data               = new stdClass();
 		$data->availability = [];
 
diff --git a/src/API/BaseRoute.php b/src/API/BaseRoute.php
index 5e13be79d..4e171fe0d 100644
--- a/src/API/BaseRoute.php
+++ b/src/API/BaseRoute.php
@@ -35,12 +35,13 @@ class BaseRoute extends WP_REST_Controller {
 	// the location of the .schema.json files locally
 	const SCHEMA_PATH = COMMONSBOOKING_PLUGIN_DIR . 'includes/commons-api-json-schema/';
 
+	/** @var string */
 	protected $schemaUrl;
 
 	/**
 	 * Register the routes for the objects of the controller.
 	 */
-	public function register_routes() {
+	public function register_routes(): void {
 		$version   = '1';
 		$namespace = COMMONSBOOKING_PLUGIN_SLUG . '/v' . $version;
 		register_rest_route(
@@ -96,7 +97,7 @@ public function register_routes() {
 	 *
 	 * @param object $data instance of stdclass or object to validate.
 	 */
-	public function validateData( $data ) {
+	public function validateData( $data ): void {
 		$validator = new Validator();
 
 		// Opis does not fetch remote $ref targets in getSchemaJson() main schema.
@@ -158,8 +159,8 @@ private function getSchemaJson(): string {
 	/**
 	 * Adds schema-fields for output to current route (needed for /.../schema endpoint)
 	 *
-	 * @param array $schema Assoc array of schema json object.
-	 * @return array
+	 * @param array<string, mixed> $schema Assoc array of schema json object.
+	 * @return array<string, mixed>
 	 */
 	public function add_additional_fields_schema( $schema ): array {
 		$schemaArray = json_decode( $this->getSchemaJson(), true );
@@ -170,11 +171,11 @@ public function add_additional_fields_schema( $schema ): array {
 	/**
 	 * Escapes JSON String for output.
 	 *
-	 * @param $string
+	 * @param string $string
 	 *
-	 * @return false|string
+	 * @return string
 	 */
-	public function escapeJsonString( $string ) {
+	public function escapeJsonString( string $string ): string {
 		return substr( wp_json_encode( $string ), 1, - 1 ) ? : '';
 	}
 
diff --git a/src/API/GBFS/BaseRoute.php b/src/API/GBFS/BaseRoute.php
index f44c3ecfc..1259ecc05 100644
--- a/src/API/GBFS/BaseRoute.php
+++ b/src/API/GBFS/BaseRoute.php
@@ -21,11 +21,11 @@ class BaseRoute extends \CommonsBooking\API\BaseRoute {
 	/**
 	 * Returns Rest Response with items.
 	 *
-	 * @param WP_REST_Request $request
+	 * @param WP_REST_Request<array<string, mixed>> $request
 	 *
 	 * @return WP_REST_Response
 	 */
-	public function get_items( $request ): WP_REST_Response {
+	public function get_items( WP_REST_Request $request ): WP_REST_Response {
 		$response                 = new stdClass();
 		$response->data           = new stdClass();
 		$response->data->stations = $this->getItemData( $request );
@@ -43,11 +43,11 @@ public function get_items( $request ): WP_REST_Response {
 	/**
 	 * Returns item data array.
 	 *
-	 * @param $request
+	 * @param WP_REST_Request<array<string, mixed>> $request
 	 *
-	 * @return array
+	 * @return array<int, mixed>
 	 */
-	public function getItemData( $request ): array {
+	public function getItemData( WP_REST_Request $request ): array {
 		$data      = [];
 		$locations = Location::get();
 
diff --git a/src/API/GBFS/Discovery.php b/src/API/GBFS/Discovery.php
index 0a31b16e9..e4aea0fae 100644
--- a/src/API/GBFS/Discovery.php
+++ b/src/API/GBFS/Discovery.php
@@ -53,7 +53,7 @@ public function get_items( $request ): WP_REST_Response {
 		return new WP_REST_Response( $response, 200 );
 	}
 
-	private function get_feed( $name ): stdClass {
+	private function get_feed( string $name ): stdClass {
 		$feed       = new stdClass();
 		$feed->name = $name;
 		$feed->url  = get_rest_url() . 'commonsbooking/v1/' . $name . '.json';
diff --git a/src/API/GBFS/StationInformation.php b/src/API/GBFS/StationInformation.php
index 807cffaee..dd03a0a03 100644
--- a/src/API/GBFS/StationInformation.php
+++ b/src/API/GBFS/StationInformation.php
@@ -26,8 +26,8 @@ class StationInformation extends BaseRoute {
 	protected $schemaUrl = COMMONSBOOKING_PLUGIN_DIR . 'includes/gbfs-json-schema/station_information.json';
 
 	/**
-	 * @param $item Location
-	 * @param $request
+	 * @param Location $item
+	 * @param WP_REST_Request<array<string, mixed>> $request
 	 *
 	 * @return WP_REST_Response
 	 * @throws \CommonsBooking\Geocoder\Exception\Exception
diff --git a/src/API/GBFS/StationStatus.php b/src/API/GBFS/StationStatus.php
index 85221c454..dc5b3524b 100644
--- a/src/API/GBFS/StationStatus.php
+++ b/src/API/GBFS/StationStatus.php
@@ -29,7 +29,7 @@ class StationStatus extends BaseRoute {
 
 	/**
 	 * @param Location $item
-	 * @param $request
+	 * @param WP_REST_Request<array<string, mixed>> $request
 	 *
 	 * @return WP_REST_Response
 	 * @throws \Exception
@@ -58,7 +58,7 @@ public function prepare_item_for_response( $item, $request ): WP_REST_Response {
 	 * @return int
 	 * @throws \Exception
 	 */
-	private function getItemCountAtLocation( $locationId ): int {
+	private function getItemCountAtLocation( int $locationId ): int {
 		$items            = Item::getByLocation( $locationId, true );
 		$nowDT            = Wordpress::getUTCDateTimeByTimestamp( current_time( 'timestamp' ) );
 		$availableCounter = 0;
diff --git a/src/API/GBFS/SystemInformation.php b/src/API/GBFS/SystemInformation.php
index 7eb4e4ad1..e4a4bce6b 100644
--- a/src/API/GBFS/SystemInformation.php
+++ b/src/API/GBFS/SystemInformation.php
@@ -22,7 +22,10 @@ class SystemInformation extends \CommonsBooking\API\BaseRoute {
 	 */
 	protected $schemaUrl = COMMONSBOOKING_PLUGIN_DIR . 'includes/gbfs-json-schema/system_information.json';
 
-	public function get_items( $request ): WP_REST_Response {
+	/**
+	 * @param WP_REST_Request<array<string, mixed>> $request
+	 */
+	public function get_items( \WP_REST_Request $request ): WP_REST_Response {
 		$tz = timezone_name_get( wp_timezone() );
 		if ( preg_match( '/^(\+|\-)0?(\d+)/', $tz, $matches ) ) {
 			$tz = 'Etc/GMT' . $matches[1] . $matches[2];
diff --git a/src/API/ItemsRoute.php b/src/API/ItemsRoute.php
index d8aa3b8c0..c34dd4723 100644
--- a/src/API/ItemsRoute.php
+++ b/src/API/ItemsRoute.php
@@ -33,11 +33,11 @@ class ItemsRoute extends BaseRoute {
 	/**
 	 * Returns raw data collection.
 	 *
-	 * @param $request
+	 * @param WP_REST_Request<array<string, mixed>> $request
 	 *
 	 * @return stdClass
 	 */
-	public function getItemData( $request ): stdClass {
+	public function getItemData( WP_REST_Request $request ): stdClass {
 		$data        = new stdClass();
 		$data->items = [];
 
@@ -61,11 +61,11 @@ public function getItemData( $request ): stdClass {
 	/**
 	 * Get a collection of items
 	 *
-	 * @param $request - Full data about the request.
+	 * @param WP_REST_Request<array<string, mixed>> $request Full data about the request.
 	 *
 	 * @return WP_Error|WP_REST_Response
 	 */
-	public function get_items( $request ) {
+	public function get_items( WP_REST_Request $request ) {
 		// get parameters from request
 		$params = $request->get_params();
 
@@ -104,23 +104,23 @@ public function get_items( $request ) {
 	/**
 	 * Get one item from the collection
 	 *
-	 * @param WP_REST_Request $request Full data about the request.
+	 * @param WP_REST_Request<array<string, mixed>> $request Full data about the request.
 	 *
 	 * @return WP_REST_Response
 	 */
-	public function get_item( $request ): WP_REST_Response {
+	public function get_item( WP_REST_Request $request ): WP_REST_Response {
 		$data = $this->getItemData( $request );
 
 		return $this->respond_with_validation( $data );
 	}
 
 	/**
-	 * @param mixed           $item
-	 * @param WP_REST_Request $request
+	 * @param mixed $item
+	 * @param WP_REST_Request<array<string, mixed>> $request
 	 *
 	 * @return WP_REST_Response
 	 */
-	public function prepare_item_for_response( $item, $request ): WP_REST_Response {
+	public function prepare_item_for_response( $item, WP_REST_Request $request ): WP_REST_Response {
 		$preparedItem              = new stdClass();
 		$preparedItem->id          = $item->ID . '';
 		$preparedItem->name        = $item->post_title;
diff --git a/src/API/LocationsRoute.php b/src/API/LocationsRoute.php
index c429278f0..8d4ea8c9e 100644
--- a/src/API/LocationsRoute.php
+++ b/src/API/LocationsRoute.php
@@ -37,29 +37,33 @@ class LocationsRoute extends BaseRoute {
 	/**
 	 * Get one item from the collection
 	 *
-	 * @param WP_REST_Request $request Full data about the request.
+	 * @param WP_REST_Request<array<string, mixed>> $request Full data about the request.
 	 *
 	 * @return WP_Error|WP_REST_Response
 	 */
-	public function get_item( $request ) {
+	public function get_item( WP_REST_Request $request ) {
 		return $this->get_items( $request );
 	}
 
 	/**
 	 * Get a collection of items
 	 *
-	 * @param WP_REST_Request $request Full data about the request.
+	 * @param WP_REST_Request<array<string, mixed>> $request Full data about the request.
 	 *
 	 * @return WP_Error|WP_REST_Response
 	 */
-	public function get_items( $request ) {
+	public function get_items( WP_REST_Request $request ) {
 		$data            = new stdClass();
 		$data->locations = $this->getItemData( $request );
 
 		return $this->respond_with_validation( $data );
 	}
 
-	public function getItemData( $request ) {
+	/**
+	 * @param WP_REST_Request<array<string, mixed>> $request
+	 * @return stdClass
+	 */
+	public function getItemData( WP_REST_Request $request ): stdClass {
 		$data       = new stdClass();
 		$data->type = 'FeatureCollection';
 
@@ -91,13 +95,13 @@ public function getItemData( $request ) {
 	}
 
 	/**
-	 * @param $item Location
-	 * @param $request
+	 * @param Location $item
+	 * @param WP_REST_Request<array<string, mixed>> $request
 	 *
 	 * @return WP_REST_Response
 	 * @throws \CommonsBooking\Geocoder\Exception\Exception
 	 */
-	public function prepare_item_for_response( $item, $request ): WP_REST_Response {
+	public function prepare_item_for_response( $item, WP_REST_Request $request ): WP_REST_Response {
 		$preparedItem             = new stdClass();
 		$preparedItem->type       = 'Feature';
 		$preparedItem->properties = new stdClass();
diff --git a/src/API/OwnersRoute.php b/src/API/OwnersRoute.php
index 0876d9ea5..e7603e162 100644
--- a/src/API/OwnersRoute.php
+++ b/src/API/OwnersRoute.php
@@ -38,11 +38,11 @@ class OwnersRoute extends BaseRoute {
 	/**
 	 * Returns raw data collection.
 	 *
-	 * @param $request
+	 * @param WP_REST_Request<array<string, mixed>> $request
 	 *
-	 * @return array
+	 * @return array<int, WP_REST_Response>
 	 */
-	public function getItemData( $request ): array {
+	public function getItemData( WP_REST_Request $request ): array {
 		$data = [];
 
 		foreach ( UserRepository::getOwners() as $owner ) {
@@ -53,12 +53,12 @@ public function getItemData( $request ): array {
 	}
 
 	/**
-	 * @param WP_User         $owner
-	 * @param WP_REST_Request $request
+	 * @param WP_User $owner
+	 * @param WP_REST_Request<array<string, mixed>> $request
 	 *
 	 * @return WP_REST_Response
 	 */
-	public function prepare_item_for_response( $owner, $request ): WP_REST_Response {
+	public function prepare_item_for_response( $owner, WP_REST_Request $request ): WP_REST_Response {
 		$ownerObject       = new stdClass();
 		$ownerObject->id   = '' . $owner->ID;
 		$ownerObject->name = get_user_meta( $owner->ID, 'first_name', true ) . ' ' . get_user_meta( $owner->ID, 'last_name', true );
@@ -85,8 +85,10 @@ public function prepare_item_for_response( $owner, $request ): WP_REST_Response
 
 	/**
 	 * Get a single item
+	 *
+	 * @param WP_REST_Request<array<string, mixed>> $request
 	 */
-	public function get_item( $request ): WP_REST_Response {
+	public function get_item( WP_REST_Request $request ): WP_REST_Response {
 		// get parameters from request
 		$params         = $request->get_params();
 		$owner          = get_user_by( 'id', $params['id'] );
@@ -99,11 +101,11 @@ public function get_item( $request ): WP_REST_Response {
 	/**
 	 * Get a collection of items
 	 *
-	 * @param WP_REST_Request $request Full data about the request.
+	 * @param WP_REST_Request<array<string, mixed>> $request Full data about the request.
 	 *
 	 * @return WP_Error|WP_REST_Response
 	 */
-	public function get_items( $request ) {
+	public function get_items( WP_REST_Request $request ) {
 		$data         = new stdClass();
 		$data->owners = $this->getItemData( $request );
 
@@ -112,8 +114,11 @@ public function get_items( $request ) {
 
 	/**
 	 * TODO investigate why we overwrite this method
+	 *
+	 * @param WP_REST_Response $itemdata
+	 * @return WP_REST_Response
 	 */
-	public function prepare_response_for_collection( $itemdata ) {
-		return $itemdata; // @phpstan-ignore return.type
+	public function prepare_response_for_collection( $itemdata ): WP_REST_Response {
+		return $itemdata;
 	}
 }
diff --git a/src/API/ProjectsRoute.php b/src/API/ProjectsRoute.php
index 6f1866357..62b344341 100644
--- a/src/API/ProjectsRoute.php
+++ b/src/API/ProjectsRoute.php
@@ -30,15 +30,19 @@ class ProjectsRoute extends BaseRoute {
 
 	/**
 	 * Get one item from the collection
+	 *
+	 * @param WP_REST_Request<array<string, mixed>> $request
 	 */
-	public function get_item( $request ) {
+	public function get_item( \WP_REST_Request $request ) {
 		return $this->get_items( $request );
 	}
 
 	/**
 	 * Get a collection of projects
+	 *
+	 * @param WP_REST_Request<array<string, mixed>> $request
 	 */
-	public function get_items( $request ): WP_REST_Response {
+	public function get_items( \WP_REST_Request $request ): WP_REST_Response {
 		$data           = new stdClass();
 		$data->projects = $this->getItemData();
 
diff --git a/src/API/Share.php b/src/API/Share.php
index 25f41d255..a4238dd60 100644
--- a/src/API/Share.php
+++ b/src/API/Share.php
@@ -12,26 +12,31 @@
  */
 class Share {
 
+	/** @var string */
 	private $name;
 
+	/** @var bool */
 	private $enabled;
 
+	/** @var string */
 	private $pushUrl;
 
+	/** @var string */
 	private $key;
 
+	/** @var string */
 	private $owner;
 
 	/**
 	 * Shares constructor.
 	 *
-	 * @param $name
-	 * @param $enabled
-	 * @param $pushUrl
-	 * @param $key
-	 * @param $owner
+	 * @param string $name
+	 * @param string $enabled
+	 * @param string $pushUrl
+	 * @param string $key
+	 * @param string $owner
 	 */
-	public function __construct( $name, $enabled, $pushUrl, $key, $owner ) {
+	public function __construct( string $name, string $enabled, string $pushUrl, string $key, string $owner ) {
 		$this->name    = $name;
 		$this->enabled = $enabled === 'on';
 		$this->pushUrl = $pushUrl;
diff --git a/src/CB/CB.php b/src/CB/CB.php
index 0cc8bb932..ccefea708 100644
--- a/src/CB/CB.php
+++ b/src/CB/CB.php
@@ -12,7 +12,7 @@
 
 class CB {
 
-	protected static $INTERNAL_DATE_FORMAT = 'd.m.Y';
+	protected static string $INTERNAL_DATE_FORMAT = 'd.m.Y';
 
 	public static function getInternalDateFormat(): string {
 		return static::$INTERNAL_DATE_FORMAT;
@@ -123,7 +123,7 @@ private static function getPostId( string $key ): ?int {
 	 * @return string|null
 	 * @throws Exception
 	 */
-	public static function lookUp( string $key, string $property, $post, $args, $sanitizeFunction ): ?string {
+	public static function lookUp( string $key, string $property, mixed $post, mixed $args, callable $sanitizeFunction ): ?string {
 		// in any case we need the post object, otherwise we cannot return anything
 		if ( ! $post ) {
 			return null;
@@ -152,7 +152,7 @@ public static function lookUp( string $key, string $property, $post, $args, $san
 	 *
 	 * @return mixed|null
 	 */
-	private static function getPostProperty( $post, $property, $args ) {
+	private static function getPostProperty( mixed $post, string $property, mixed $args ): mixed {
 		$result = null;
 
 		$postId = is_int( $post ) ? $post : $post->ID;
@@ -187,7 +187,7 @@ private static function getPostProperty( $post, $property, $args ) {
 	 * @return int|mixed|null
 	 * @throws Exception
 	 */
-	private static function getUserProperty( $post, string $property, $args ) {
+	private static function getUserProperty( \WP_Post|\WP_User $post, string $property, mixed $args ): mixed {
 		$result = null;
 
 		$cb_user = self::getUserFromObject( $post );
@@ -213,7 +213,7 @@ private static function getUserProperty( $post, string $property, $args ) {
 	 * @return false|WP_User
 	 * @throws Exception
 	 */
-	private static function getUserFromObject( $object ) {
+	private static function getUserFromObject( mixed $object ): \WP_User|false {
 		// Check if $post is of type WP_Post, then we're using Author as User
 		if ( $object instanceof WP_Post ) {
 			$userID = intval( $object->post_author );
diff --git a/src/CB/CB1UserFields.php b/src/CB/CB1UserFields.php
index ab13df649..58566e37d 100644
--- a/src/CB/CB1UserFields.php
+++ b/src/CB/CB1UserFields.php
@@ -19,7 +19,7 @@ class CB1UserFields {
 	 */
 	private array $registration_fields;
 	/**
-	 * @var array|array[]
+	 * @var array<string, array<string, string>>
 	 */
 	private array $extra_profile_fields;
 	/**
@@ -27,7 +27,7 @@ class CB1UserFields {
 	 */
 	private array $registration_fields_required; // @phpstan-ignore property.onlyWritten
 	/**
-	 * @var array|array[]
+	 * @var array<string, array<string, string>>
 	 */
 	private array $user_fields;
 	/**
@@ -116,7 +116,7 @@ public function __construct() {
 	/**
 	 * Get the additional User fields
 	 *
-	 * @return array
+	 * @return array<string, array<string, string>>
 	 * @since    0.6.
 	 */
 	public function get_extra_profile_fields(): array {
@@ -131,7 +131,7 @@ public function get_extra_profile_fields(): array {
 	* @return    object
 	*/
 
-	public function registration_add_fields() {
+	public function registration_add_fields(): void {
 
 		foreach ( $this->user_fields as $field ) {
 			$row = ( ! empty( $_POST[ $field['field_name'] ] ) ) ? sanitize_text_field( trim( $_POST[ $field['field_name'] ] ) ) : '';
@@ -195,7 +195,7 @@ public function get_termsservices_string(): string {
 		return $string;
 	}
 
-	public function registration_set_errors( $errors, $username, $email ) {
+	public function registration_set_errors( \WP_Error $errors, string $username, string $email ): \WP_Error {
 
 		foreach ( $this->user_fields as $field ) {
 			if ( $field['type'] == 'checkbox' ) {
@@ -212,7 +212,7 @@ public function registration_set_errors( $errors, $username, $email ) {
 		return $errors;
 	}
 
-	public function registration_add_meta( $user_id ) {
+	public function registration_add_meta( int $user_id ): void {
 
 		foreach ( $this->user_fields as $field ) {
 			if ( ! empty( $_POST[ $field['field_name'] ] ) ) {
@@ -229,7 +229,7 @@ public function registration_add_meta( $user_id ) {
 	 * @since    2.10 deprecated (cb_object_to_array is unspecified)
 	 * @since    0.6
 	 */
-	public function set_basic_user_vars( $user_id ) {
+	public function set_basic_user_vars( int $user_id ): void {
 		$user_basic = get_user_by( 'id', $user_id );
 		$user_meta  = get_user_meta( $user_id );
 
@@ -250,7 +250,7 @@ public function set_basic_user_vars( $user_id ) {
 	 *
 	 * @since    0.5.3
 	 */
-	public function add_user_vars( $key, $value ) {
+	public function add_user_vars( string $key, mixed $value ): void {
 
 		$this->user_vars[ $key ] = $value;
 	}
@@ -260,7 +260,7 @@ public function add_user_vars( $key, $value ) {
 	 *
 	 * @since    0.2
 	 */
-	public function show_extra_profile_fields( $user ) {
+	public function show_extra_profile_fields( \WP_User $user ): void {
 
 		?>
 
@@ -306,7 +306,7 @@ class="regular-text"/><br/>
 	 *
 	 * @since    0.2
 	 */
-	public function save_extra_profile_fields( $user_id ) {
+	public function save_extra_profile_fields( int $user_id ): void {
 		if ( current_user_can( 'edit_user', $user_id ) ) {
 			$phone   = sanitize_text_field( $_POST['phone'] );
 			$address = sanitize_text_field( $_POST['address'] );
diff --git a/src/Helper/API.php b/src/Helper/API.php
index e678fb476..06949a583 100644
--- a/src/Helper/API.php
+++ b/src/Helper/API.php
@@ -12,7 +12,7 @@ class API {
 	/**
 	 * Triggers requests to all shares with push url.
 	 */
-	public static function triggerPushUrls() {
+	public static function triggerPushUrls(): void {
 		$apiShares = ApiShares::getAll();
 
 		foreach ( $apiShares as $apiShare ) {
@@ -27,7 +27,7 @@ public static function triggerPushUrls() {
 	 *
 	 * @param Share $share
 	 */
-	public static function triggerPushUrl( Share $share ) {
+	public static function triggerPushUrl( Share $share ): void {
 		$requestData = [
 			'API_KEY' => $share->getKey(),
 			'OWNER' => $share->getOwner(),
diff --git a/src/Helper/Helper.php b/src/Helper/Helper.php
index d8f57cb72..fbc8ebf50 100644
--- a/src/Helper/Helper.php
+++ b/src/Helper/Helper.php
@@ -80,11 +80,11 @@ public static function getLastFullHourTimestamp() {
 	/**
 	 * Returns timestamp of last full day, needed to get more cache hits.
 	 *
-	 * @param $timestamp
+	 * @param int|null $timestamp
 	 *
-	 * @return int|mixed|null
+	 * @return int
 	 */
-	public static function getLastFullDayTimestamp( $timestamp = null ) {
+	public static function getLastFullDayTimestamp( ?int $timestamp = null ): int {
 		if ( $timestamp === null ) {
 			$timestamp = current_time( 'timestamp' );
 		}
@@ -95,13 +95,13 @@ public static function getLastFullDayTimestamp( $timestamp = null ) {
 	/**
 	 * Returns CB custom post type if possible.
 	 *
-	 * @param $post
-	 * @param $type
+	 * @param mixed $post
+	 * @param string $type
 	 *
 	 * @return Booking|Item|Location|mixed
 	 * @throws \Exception
 	 */
-	public static function castToCBCustomType( $post, $type ) {
+	public static function castToCBCustomType( mixed $post, string $type ): mixed {
 		if ( $type == \CommonsBooking\Wordpress\CustomPostType\Booking::$postType ) {
 			$post = new Booking( $post->ID );
 		}
@@ -121,9 +121,9 @@ public static function castToCBCustomType( $post, $type ) {
 	 * NOTE: When performance issues arise, this operation can be implemented
 	 * faster with an interval tree data structure
 	 *
-	 * @param array $array_of_ranges Array of one or more ranges.
+	 * @param array<int, array<string, mixed>> $array_of_ranges Array of one or more ranges.
 	 *
-	 * @return array - Array of overlapping ranges.
+	 * @return array<int, array<string, mixed>> Array of overlapping ranges.
 	 */
 	public static function mergeRangesToBookableDates( array $array_of_ranges ): array {
 		$interval_open = function ( $interval_value ): bool {
diff --git a/src/Helper/Wordpress.php b/src/Helper/Wordpress.php
index 43256ccde..cb328323f 100644
--- a/src/Helper/Wordpress.php
+++ b/src/Helper/Wordpress.php
@@ -13,7 +13,7 @@
 class Wordpress {
 
 	/**
-	 * @return array
+	 * @return array<int, string>
 	 */
 	public static function getPageListTitle(): array {
 		$pages    = get_pages();
@@ -31,11 +31,11 @@ public static function getPageListTitle(): array {
 	/**
 	 * Flatten array and return it.
 	 *
-	 * @param $posts
+	 * @param object[] $posts
 	 *
-	 * @return array|array[]|null[]|\WP_Post[]
+	 * @return array<int, \WP_Post|null>
 	 */
-	public static function flattenWpdbResult( $posts ): array {
+	public static function flattenWpdbResult( array $posts ): array {
 		return array_map(
 			function ( $post ) {
 				return get_post( $post->ID );
@@ -45,22 +45,22 @@ function ( $post ) {
 	}
 
 	/**
-	 * @param $dateString
+	 * @param string $dateString
 	 *
-	 * @return bool|false
+	 * @return bool
 	 */
-	public static function isValidDateString( $dateString ): bool {
+	public static function isValidDateString( string $dateString ): bool {
 		return preg_match( '/^[0-9]{4}\-[0-9]{2}\-[0-9]{2}$/i', $dateString ) === 1;
 	}
 
 	/**
 	 * Returns array with IDs.
 	 *
-	 * @param $posts
+	 * @param object[] $posts
 	 *
-	 * @return array
+	 * @return int[]
 	 */
-	public static function getPostIdArray( $posts ): array {
+	public static function getPostIdArray( array $posts ): array {
 		return array_map(
 			function ( $post ) {
 				return intval( $post->ID );
@@ -73,11 +73,11 @@ function ( $post ) {
 	 * Returns all post ids which are in relation to $postId.
 	 * Why? Needed to get tags for cache invalidation.
 	 *
-	 * @param $postId
+	 * @param int $postId
 	 *
-	 * @return array|string[]
+	 * @return string[]
 	 */
-	public static function getRelatedPostIds( $postId ): array {
+	public static function getRelatedPostIds( int $postId ): array {
 		$postIds = [];
 		$post    = get_post( $postId );
 
@@ -108,12 +108,12 @@ public static function getRelatedPostIds( $postId ): array {
 	/**
 	 * Returns all post ids in relation to $postId.
 	 *
-	 * @param $postId
+	 * @param int $postId
 	 *
-	 * @return mixed
+	 * @return int[]
 	 * @throws \CommonsBooking\Psr\Cache\InvalidArgumentException
 	 */
-	public static function getRelatedPostsIdsForLocation( $postId ) {
+	public static function getRelatedPostsIdsForLocation( int $postId ): array {
 		$timeframes   = \CommonsBooking\Repository\Timeframe::get( [ $postId ] );
 		$restrictions = \CommonsBooking\Repository\Restriction::get( [ $postId ] );
 		return array_merge(
@@ -127,12 +127,12 @@ public static function getRelatedPostsIdsForLocation( $postId ) {
 	 * Returns all post ids in relation to $postId.
 	 * CAREFUL: This will not get the location that the item is in relation to.
 	 *
-	 * @param $postId
+	 * @param int $postId
 	 *
-	 * @return array
+	 * @return int[]
 	 * @throws \CommonsBooking\Psr\Cache\InvalidArgumentException
 	 */
-	public static function getRelatedPostsIdsForItem( $postId ): array {
+	public static function getRelatedPostsIdsForItem( int $postId ): array {
 		$timeframes   = \CommonsBooking\Repository\Timeframe::get( [], [ $postId ] );
 		$restrictions = \CommonsBooking\Repository\Restriction::get( [], [ $postId ] );
 		return array_merge(
@@ -145,12 +145,12 @@ public static function getRelatedPostsIdsForItem( $postId ): array {
 	/**
 	 * Returns all post ids in relation to $postId.
 	 *
-	 * @param $postId
+	 * @param int $postId
 	 *
-	 * @return array
+	 * @return int[]
 	 * @throws \Exception
 	 */
-	public static function getRelatedPostsIdsForTimeframe( $postId ): array {
+	public static function getRelatedPostsIdsForTimeframe( int $postId ): array {
 		$timeframe = new Timeframe( $postId );
 		$ids       = [ $postId ];
 		return array_merge( $ids, $timeframe->getItemIDs(), $timeframe->getLocationIDs() );
@@ -159,12 +159,12 @@ public static function getRelatedPostsIdsForTimeframe( $postId ): array {
 	/**
 	 * Returns all post ids in relation to $postId.
 	 *
-	 * @param $postId
+	 * @param int $postId
 	 *
-	 * @return array
+	 * @return int[]
 	 * @throws \Exception
 	 */
-	public static function getRelatedPostsIdsForBooking( $postId ): array {
+	public static function getRelatedPostsIdsForBooking( int $postId ): array {
 		$booking = new \CommonsBooking\Model\Booking( $postId );
 		$ids     = [ $postId ];
 
@@ -184,12 +184,12 @@ public static function getRelatedPostsIdsForBooking( $postId ): array {
 	/**
 	 * Returns all post ids in relation to $postId.
 	 *
-	 * @param $postId
+	 * @param int $postId
 	 *
-	 * @return array
+	 * @return int[]
 	 * @throws \CommonsBooking\Psr\Cache\InvalidArgumentException
 	 */
-	public static function getRelatedPostsIdsForRestriction( $postId ): array {
+	public static function getRelatedPostsIdsForRestriction( int $postId ): array {
 		$restriction = new \CommonsBooking\Model\Restriction( $postId );
 
 		// Restriction itself
@@ -217,13 +217,13 @@ public static function getRelatedPostsIdsForRestriction( $postId ): array {
 	/**
 	 * Returns a list of cache tags related to $posts, $items and $locations.
 	 *
-	 * @param $posts
-	 * @param array $items
-	 * @param array $locations
+	 * @param array<int, \WP_Post|Timeframe|\CommonsBooking\Model\Booking> $posts
+	 * @param array<int, int|string> $items
+	 * @param array<int, int|string> $locations
 	 *
-	 * @return array
+	 * @return array<int, int|string>
 	 */
-	public static function getTags( $posts, array $items = [], array $locations = [] ): array {
+	public static function getTags( array $posts, array $items = [], array $locations = [] ): array {
 		$itemsAndLocations = self::getLocationAndItemIdsFromPosts( $posts );
 
 		if ( ! count( $items ) && ! count( $locations ) ) {
@@ -247,9 +247,9 @@ public static function getTags( $posts, array $items = [], array $locations = []
 	 * The only posts that have items / locations assinged are timeframes and bookings.
 	 * Any other posts are skipped.
 	 *
-	 * @param $posts
+	 * @param array<int, \WP_Post|Timeframe|\CommonsBooking\Model\Booking> $posts
 	 *
-	 * @return array
+	 * @return int[]
 	 */
 	public static function getLocationAndItemIdsFromPosts( array $posts ): array {
 		$itemsAndLocations = [];
@@ -313,14 +313,14 @@ public static function convertTimestampToUTCDatetime( $timestamp ) {
 		return $dto;
 	}
 
-	public static function getUTCDateTime( $datetime = 'now' ): DateTime {
+	public static function getUTCDateTime( string $datetime = 'now' ): DateTime {
 		$dto = new DateTime( $datetime );
 		$dto->setTimezone( new \DateTimeZone( 'UTC' ) );
 
 		return $dto;
 	}
 
-	public static function getLocalDateTime( $timestamp ): DateTime {
+	public static function getLocalDateTime( int $timestamp ): DateTime {
 		$dto = new DateTime();
 		$dto->setTimestamp(
 			$timestamp
diff --git a/src/Map/BaseShortcode.php b/src/Map/BaseShortcode.php
index 65a982fbe..b5241dca1 100644
--- a/src/Map/BaseShortcode.php
+++ b/src/Map/BaseShortcode.php
@@ -14,7 +14,7 @@ final public function __construct() { }
 	/**
 	 * The shortcode handler - load all the needed assets and render the map container
 	 *
-	 * @param array  $atts attributes for parametrization.
+	 * @param array<string|int, mixed> $atts attributes for parametrization.
 	 * @param string $content content to display, if shortcode implementation allows to.
 	 **/
 	public static function execute( array $atts, string $content = '' ): string {
@@ -40,7 +40,15 @@ public static function execute( array $atts, string $content = '' ): string {
 		$instance->inject_script( $cb_map_id );
 		return $instance->create_container( $cb_map_id, $attrs, $options, $content );
 	}
-	abstract protected function parse_attributes( $atts );
-	abstract protected function inject_script( $cb_map_id );
-	abstract protected function create_container( $cb_map_id, $attrs, $options, $content );
+	/**
+	 * @param array<string|int, mixed> $atts
+	 * @return array<string, mixed>
+	 */
+	abstract protected function parse_attributes( array $atts ): array;
+	abstract protected function inject_script( int $cb_map_id ): void;
+	/**
+	 * @param array<string, mixed> $attrs
+	 * @param array<int, mixed> $options
+	 */
+	abstract protected function create_container( int $cb_map_id, array $attrs, array $options, string $content ): string;
 }
diff --git a/src/Map/LocationMapAdmin.php b/src/Map/LocationMapAdmin.php
index 366acb298..012525b2f 100644
--- a/src/Map/LocationMapAdmin.php
+++ b/src/Map/LocationMapAdmin.php
@@ -9,7 +9,7 @@ class LocationMapAdmin {
 	/**
 	 * load the location administration map
 	 */
-	public function load_location_map_admin() {
+	public function load_location_map_admin(): void {
 		if ( COMMONSBOOKING_PLUGIN_DIR ) {
 			// render map
 			add_action( 'cmb2_render_cb_map', array( Map::class, 'render_cb_map' ), 10, 5 );
diff --git a/src/Map/MapData.php b/src/Map/MapData.php
index b59c31d0b..a1190f4ee 100644
--- a/src/Map/MapData.php
+++ b/src/Map/MapData.php
@@ -6,7 +6,7 @@
 use CommonsBooking\Model\Map;
 
 class MapData {
-	public static function geo_search() {
+	public static function geo_search(): void {
 		if ( isset( $_POST['query'] ) && $_POST['cb_map_id'] ) {
 			$map = new Map( $_POST['cb_map_id'] );
 
@@ -74,7 +74,7 @@ public static function geo_search() {
 	/**
 	 * the ajax request handler for locations
 	 **/
-	public static function get_locations() {
+	public static function get_locations(): void {
 		// handle local/import map
 		if ( isset( $_POST['cb_map_id'] ) ) {
 			check_ajax_referer( 'cb_map_locations', 'nonce' );
@@ -126,9 +126,10 @@ public static function get_locations() {
 	/**
 	 * Returns configured item terms
 	 *
-	 * @return array
+	 * @param array<string, mixed> $settings
+	 * @return array<int, mixed>
 	 */
-	public static function getItemCategoryTerms( $settings ): array {
+	public static function getItemCategoryTerms( array $settings ): array {
 		$terms = [];
 
 		foreach ( $settings['filter_cb_item_categories'] as $categoryGroup ) {
@@ -144,8 +145,10 @@ public static function getItemCategoryTerms( $settings ): array {
 
 	/**
 	 * get the settings for the frontend of the map with given id
+	 *
+	 * @return array<string, mixed>
 	 **/
-	public static function get_settings( $cb_map_id ): array {
+	public static function get_settings( int $cb_map_id ): array {
 		$map                = new Map( $cb_map_id );
 		$date_min           = Wordpress::getUTCDateTime();
 		$date_min           = $date_min->format( 'Y-m-d' );
diff --git a/src/Map/MapFilter.php b/src/Map/MapFilter.php
index 7c3f5e5a4..8f2a9be61 100644
--- a/src/Map/MapFilter.php
+++ b/src/Map/MapFilter.php
@@ -4,7 +4,11 @@
 
 class MapFilter {
 
-	protected static function check_item_terms_against_categories( $item_terms, $category_groups ): bool {
+	/**
+	 * @param array<int, mixed> $item_terms
+	 * @param array<int, mixed> $category_groups
+	 */
+	protected static function check_item_terms_against_categories( array $item_terms, array $category_groups ): bool {
 		$valid_groups_count = 0;
 
 		foreach ( $category_groups as $group ) {
diff --git a/src/Map/MapItemAvailable.php b/src/Map/MapItemAvailable.php
index f0144dee5..10c057adf 100644
--- a/src/Map/MapItemAvailable.php
+++ b/src/Map/MapItemAvailable.php
@@ -44,14 +44,14 @@ class MapItemAvailable {
 	const OUT_OF_TIMEFRAME = 'no-timeframe';
 
 	/**
-	 * @param $locations
-	 * @param $date_start
-	 * @param $date_end
+	 * @param array<int|string, mixed> $locations
+	 * @param string $date_start
+	 * @param string $date_end
 	 *
-	 * @return mixed
+	 * @return array<int|string, mixed>
 	 * @throws Exception
 	 */
-	public static function create_items_availabilities( $locations, $date_start, $date_end ) {
+	public static function create_items_availabilities( array $locations, string $date_start, string $date_end ): array {
 
 		$startDay = new Day( $date_start );
 		$endDay   = new Day( $date_end );
@@ -104,12 +104,12 @@ public static function create_items_availabilities( $locations, $date_start, $da
 	 *  This logic should resemble the logic in the @see \CommonsBooking\View\Calendar::processSlot() method because
 	 *  otherwise days would be mapped differently throughout the plugin.
 	 *
-	 * @param $calendarData
-	 * @param $availabilities
+	 * @param array<string, mixed> $calendarData
+	 * @param array<int, array<string, mixed>> $availabilities
 	 *
-	 * @return mixed
+	 * @return array<int, array<string, mixed>>
 	 */
-	protected static function markDaysInTimeframe( $calendarData, $availabilities ) {
+	protected static function markDaysInTimeframe( array $calendarData, array $availabilities ): array {
 		// mark days which are inside a timeframe
 		foreach ( $availabilities as &$availability ) {
 			if ( array_key_exists( $availability['date'], $calendarData['days'] ) ) {
diff --git a/src/Map/MapShortcode.php b/src/Map/MapShortcode.php
index a034da6d1..d8b21a28f 100644
--- a/src/Map/MapShortcode.php
+++ b/src/Map/MapShortcode.php
@@ -8,18 +8,23 @@
  * Shortcode for the legacy map with the old non-responsive standard leaflet style.
  */
 class MapShortcode extends BaseShortcode {
-	protected function create_container( $cb_map_id, $attrs, $options, $content ) {
+	/**
+	 * @param array<string, mixed> $attrs
+	 * @param array<int, mixed> $options
+	 */
+	protected function create_container( int $cb_map_id, array $attrs, array $options, string $content ): string {
 		$map        = new Map( $cb_map_id );
 		$map_height = $map->getMeta( 'map_height' );
 
-		return '<div id="cb-map-' . esc_attr( $cb_map_id ) . '" class="cb-wrapper cb-leaflet-map" style="width: 100%; height: ' . esc_attr( $map_height ) . 'px;"></div>';
+		return '<div id="cb-map-' . esc_attr( (string) $cb_map_id ) . '" class="cb-wrapper cb-leaflet-map" style="width: 100%; height: ' . esc_attr( (string) $map_height ) . 'px;"></div>';
 	}
 
-	protected function parse_attributes( $atts ) {
+	/** @return array<string, mixed> */
+	protected function parse_attributes( array $atts ): array {
 		return shortcode_atts( array( 'id' => 0 ), $atts );
 	}
 
-	protected function inject_script( $cb_map_id ) {
+	protected function inject_script( int $cb_map_id ): void {
 		wp_add_inline_script(
 			'cb-map-shortcode',
 			'jQuery(document).ready(function ($) {
@@ -37,7 +42,8 @@ protected function inject_script( $cb_map_id ) {
 	/**
 	 * get the translations for the frontend
 	 **/
-	private function get_translation( $cb_map_id ): array {
+	/** @return array<string, string> */
+	private function get_translation( int $cb_map_id ): array {
 		$map                            = new Map( $cb_map_id );
 		$label_location_opening_hours   = $map->getMeta( 'label_location_opening_hours' );
 		$label_location_contact         = $map->getMeta( 'label_location_contact' );
diff --git a/src/Map/SearchShortcode.php b/src/Map/SearchShortcode.php
index 566f020d7..64f54f525 100644
--- a/src/Map/SearchShortcode.php
+++ b/src/Map/SearchShortcode.php
@@ -6,9 +6,11 @@
  * Short code for a multi-widget with map, search and table capabilities.
  */
 class SearchShortcode extends BaseShortcode {
-	protected $processed_map_ids = [];
+	/** @var int[] */
+	protected array $processed_map_ids = [];
 
-	protected function parse_attributes( $atts ) {
+	/** @return array<string, mixed> */
+	protected function parse_attributes( array $atts ): array {
 		return shortcode_atts(
 			[
 				'id' => null,
@@ -18,12 +20,16 @@ protected function parse_attributes( $atts ) {
 		);
 	}
 
-	protected function inject_script( $cb_map_id ) {
+	protected function inject_script( int $cb_map_id ): void {
 		wp_enqueue_style( 'cb-commons-search' );
 		wp_enqueue_script( 'cb-commons-search' );
 	}
 
-	protected function create_container( $cb_map_id, $attrs, $options, $content ) {
+	/**
+	 * @param array<string, mixed> $attrs
+	 * @param array<int, mixed> $options
+	 */
+	protected function create_container( int $cb_map_id, array $attrs, array $options, string $content ): string {
 		// Ensure that the api and config object are only created once per page and per map
 		if ( ! in_array( $cb_map_id, $this->processed_map_ids ) ) {
 			$settings                  = MapData::get_settings( $cb_map_id );
@@ -73,7 +79,12 @@ protected function create_container( $cb_map_id, $attrs, $options, $content ) {
 	}
 }
 
-function pop_key( &$array, $key ) {
+/**
+ * @param array<string, mixed> $array
+ * @param string $key
+ * @return mixed
+ */
+function pop_key( array &$array, string $key ): mixed {
 	$value = $array[ $key ];
 	unset( $array[ $key ] );
 	return $value;
diff --git a/src/Messages/BookingCodesMessage.php b/src/Messages/BookingCodesMessage.php
index 4a461e06f..2e90cfb02 100644
--- a/src/Messages/BookingCodesMessage.php
+++ b/src/Messages/BookingCodesMessage.php
@@ -20,7 +20,8 @@
  */
 class BookingCodesMessage extends Message {
 
-	protected $validActions = [ 'codes' ];
+	/** @var string[] */
+	protected array $validActions = [ 'codes' ];
 	protected $to;
 	private ?int $tsFrom;
 	private ?int $tsTo;
@@ -44,22 +45,22 @@ public function __construct( int $postId, string $action, int $tsFrom, int $tsTo
 
 	/**
 	 * prepares Message and sends by E-mail
-	 *
-	 * @return bool    true if message was sent, false otherwise. If the message is not sent, an error is raised.
 	 */
-	public function sendMessage(): bool {
+	public function sendMessage(): void {
 		$timeframeId = (int) $this->getPostId();
 		$timeframe   = new Timeframe( $timeframeId );
 
 		if ( ! $this->prepareReceivers( $timeframe ) ) {
-			return $this->raiseError(
+			$this->raiseError(
 				__( 'Unable to send Emails. No location email(s) configured, check location', 'commonsbooking' )
 			);
+			return;
 		}
 
 		$bookingCodes = BookingCodes::getCodes( $timeframeId, $this->tsFrom, $this->tsTo );
 		if ( empty( $bookingCodes ) ) {
-			return $this->raiseError( __( 'Could not find booking codes for this timeframe/period', 'commonsbooking' ) );
+			$this->raiseError( __( 'Could not find booking codes for this timeframe/period', 'commonsbooking' ) );
+			return;
 		}
 
 		$bookingTable = \CommonsBooking\View\BookingCodes::renderTableFor( 'email', $bookingCodes );
@@ -136,8 +137,6 @@ public function sendMessage(): bool {
 		}
 
 		remove_action( 'commonsbooking_mail_sent', array( $this, 'updateEmailSent' ), 5 );
-
-		return true;
 	}
 
 	/**
@@ -149,7 +148,7 @@ public function sendMessage(): bool {
 	 *
 	 * @return void
 	 */
-	public function updateEmailSent( $action, $result ) {
+	public function updateEmailSent( string $action, mixed $result ): void {
 		if ( $this->action != $action ) {
 			return;
 		}
@@ -162,7 +161,7 @@ public function updateEmailSent( $action, $result ) {
 	/**
 	 * filter commonsbooking_mail_to for adding multiple to email addresses
 	 *
-	 * @return array
+	 * @return array<int, string>
 	 */
 	public function addMultiTo(): array {
 		$to = array();
@@ -201,7 +200,7 @@ protected function prepareReceivers( Timeframe $timeframe ): bool {
 	 *
 	 * @param BookingCode[] $bookingCodes   List of BookingCode objects
 	 *
-	 * @return array
+	 * @return array<string, mixed>
 	 */
 	protected function getIcalAttachment( array $bookingCodes ): array {
 		$calendar = new iCalendar();
diff --git a/src/Messages/BookingMessage.php b/src/Messages/BookingMessage.php
index cdddd044a..e79b36ea2 100644
--- a/src/Messages/BookingMessage.php
+++ b/src/Messages/BookingMessage.php
@@ -18,9 +18,9 @@ class BookingMessage extends Message {
 	 *
 	 * @var string[]
 	 */
-	protected $validActions = [ 'confirmed', 'canceled' ];
+	protected array $validActions = [ 'confirmed', 'canceled' ];
 
-	public function sendMessage() {
+	public function sendMessage(): void {
 		/** @var \CommonsBooking\Model\Booking $booking */
 		$booking = Booking::getPostById( $this->getPostId() );
 
diff --git a/src/Messages/BookingReminderMessage.php b/src/Messages/BookingReminderMessage.php
index 9c14d665c..50fc06b1e 100644
--- a/src/Messages/BookingReminderMessage.php
+++ b/src/Messages/BookingReminderMessage.php
@@ -14,17 +14,15 @@
  */
 class BookingReminderMessage extends Message {
 
-	/**
-	 * @var array|string[]
-	 */
-	protected $validActions = [ 'pre-booking-reminder', 'post-booking-notice' ];
+	/** @var string[] */
+	protected array $validActions = [ 'pre-booking-reminder', 'post-booking-notice' ];
 
 	/**
 	 * Sends reminder message.
 	 *
 	 * @throws \Exception
 	 */
-	public function sendMessage() {
+	public function sendMessage(): void {
 		/** @var \CommonsBooking\Model\Booking $booking */
 		$booking      = Booking::getPostById( $this->getPostId() );
 		$booking_user = get_userdata( (int) $this->getPost()->post_author );
diff --git a/src/Messages/LocationBookingReminderMessage.php b/src/Messages/LocationBookingReminderMessage.php
index 98c499313..7396c8bae 100644
--- a/src/Messages/LocationBookingReminderMessage.php
+++ b/src/Messages/LocationBookingReminderMessage.php
@@ -16,15 +16,13 @@
  */
 class LocationBookingReminderMessage extends Message {
 
-	/**
-	 * @var array|string[]
-	 */
-	protected $validActions = [ 'booking-start-location-reminder', 'booking-end-location-reminder' ];
+	/** @var string[] */
+	protected array $validActions = [ 'booking-start-location-reminder', 'booking-end-location-reminder' ];
 
 	/**
 	 * Sends reminder message.
 	 */
-	public function sendMessage() {
+	public function sendMessage(): void {
 		/** @var \CommonsBooking\Model\Booking $booking */
 		$booking      = Booking::getPostById( $this->getPostId() );
 		$booking_user = get_userdata( (int) $this->getPost()->post_author );
diff --git a/src/Messages/Message.php b/src/Messages/Message.php
index a2ae571d5..fb908b6aa 100644
--- a/src/Messages/Message.php
+++ b/src/Messages/Message.php
@@ -15,16 +15,16 @@ abstract class Message {
 	/**
 	 * The actions that are valid for this message. Usually a string.
 	 *
-	 * @var array
+	 * @var string[]
 	 */
-	protected $validActions = [];
+	protected array $validActions = [];
 
 	/**
 	 * The action that is used for this message. Needs to be contained in $validActions
 	 *
 	 * @var string
 	 */
-	protected $action;
+	protected string $action;
 
 	/**
 	 * The post that this message is about
@@ -69,9 +69,9 @@ abstract class Message {
 	 *    'type' => File MIME type (if left unspecified, PHPMailer will try to work it out from the file name)
 	 *    'disposition' => Disposition to use (defaults to 'attachment')
 	 *
-	 * @var array
+	 * @var array<string, mixed>
 	 */
-	protected $attachment = [];
+	protected array $attachment = [];
 	/**
 	 * @var int
 	 */
@@ -81,7 +81,7 @@ abstract class Message {
 	 * @param $postId
 	 * @param $action
 	 */
-	public function __construct( $postId, $action ) {
+	public function __construct( int $postId, string $action ) {
 		$this->postId = $postId;
 
 		global $post;
@@ -90,7 +90,7 @@ public function __construct( $postId, $action ) {
 		$this->action = $action;
 	}
 
-	public function getAction() {
+	public function getAction(): string {
 		return $this->action;
 	}
 
@@ -114,7 +114,8 @@ public function getTo() {
 		return apply_filters( 'commonsbooking_mail_to', $recipient, $messageAction );
 	}
 
-	public function getHeaders() {
+	/** @return string[]|null */
+	public function getHeaders(): ?array {
 		return $this->headers;
 	}
 
@@ -161,7 +162,7 @@ public function getBody() {
 	/**
 	 * Return array of attachment
 	 *
-	 * @return array
+	 * @return array<string, mixed>
 	 */
 	public function getAttachment(): array {
 		$attachment    = $this->attachment;
@@ -186,7 +187,7 @@ public function getAttachment(): array {
 	 * @param string           $from_headers From-Header (From:xxx)
 	 * @param string|null      $bcc_adresses comma separated string with e-mail adresses
 	 * @param object[]         $objects objects used in parse template function
-	 * @param array|null       $attachment
+	 * @param array<string, mixed>|null $attachment
 	 */
 	protected function prepareMail(
 		MessageRecipient $recipientUser,
@@ -260,7 +261,7 @@ public function sendNotificationMail() {
 		do_action( 'commonsbooking_mail_sent', $this->getAction(), $result );
 	}
 
-	abstract public function sendMessage();
+	abstract public function sendMessage(): void;
 
 	/**
 	 * Only send mail if action is valid
@@ -292,18 +293,18 @@ public function getPostId() {
 	}
 
 	/**
-	 * @param array $address_array
+	 * @param string[] $address_array
 	 *
 	 * @return void
 	 */
-	protected function add_bcc( array $address_array ) {
+	protected function add_bcc( array $address_array ): void {
 		// sanitize emails
 		$address_array   = array_filter( array_map( 'sanitize_email', $address_array ) );
 		$this->headers[] = sprintf( 'BCC:%s', implode( ',', $address_array ) );
 	}
 
 	/**
-	 * @return array
+	 * @return string[]
 	 */
 	public function getValidActions(): array {
 		return $this->validActions;
@@ -323,7 +324,11 @@ public function getValidActions(): array {
 	 *
 	 * @see https://gist.github.com/thomasfw/5df1a041fd8f9c939ef9d88d887ce023/
 	 */
-	public function addStringAttachments( $atts ) {
+	/**
+	 * @param array<string, mixed> $atts
+	 * @return array<string, mixed>
+	 */
+	public function addStringAttachments( array $atts ): array {
 		$attachment_arrays = [];
 		if ( ! empty( $atts['attachments'] ) ) {
 			$attachments = $atts['attachments'];
diff --git a/src/Messages/RestrictionMessage.php b/src/Messages/RestrictionMessage.php
index b1a43ba98..75cad4d2b 100644
--- a/src/Messages/RestrictionMessage.php
+++ b/src/Messages/RestrictionMessage.php
@@ -14,17 +14,16 @@
  */
 class RestrictionMessage extends Message {
 
-	protected $user;
+	protected \WP_User $user;
 
-	protected $restriction;
+	protected Restriction $restriction;
 
-	protected $action;
-
-	protected $booking;
+	protected Booking $booking;
 
 	protected bool $firstMessage;
 
-	protected $validActions = [
+	/** @var string[] */
+	protected array $validActions = [
 		Restriction::TYPE_REPAIR,
 		Restriction::TYPE_HINT,
 	];
@@ -35,7 +34,7 @@ class RestrictionMessage extends Message {
 	 * @param $booking Booking
 	 * @param $action
 	 */
-	public function __construct( $restriction, $user, Booking $booking, $action, bool $firstMessage = false ) {
+	public function __construct( Restriction $restriction, \WP_User $user, Booking $booking, string $action, bool $firstMessage = false ) {
 		$this->restriction  = $restriction;
 		$this->user         = $user;
 		$this->booking      = $booking;
@@ -46,7 +45,7 @@ public function __construct( $restriction, $user, Booking $booking, $action, boo
 	/**
 	 * Sends mails related to restriction type and state.
 	 */
-	public function sendMessage() {
+	public function sendMessage(): void {
 		if ( $this->getRestriction()->isActive() ) {
 			if ( $this->getRestriction()->getType() == Restriction::TYPE_HINT ) {
 				// send hint mail
@@ -66,7 +65,7 @@ public function sendMessage() {
 	/**
 	 * Sends hint mail.
 	 */
-	protected function sendHintMail() {
+	protected function sendHintMail(): void {
 		$body    = Settings::getOption( 'commonsbooking_options_restrictions', 'restrictions-hint-body' );
 		$subject = Settings::getOption( 'commonsbooking_options_restrictions', 'restrictions-hint-subject', 'sanitize_text_field' );
 
@@ -81,7 +80,7 @@ protected function sendHintMail() {
 	/**
 	 * Sends repair mail.
 	 */
-	protected function sendRepairMail() {
+	protected function sendRepairMail(): void {
 		$body    = Settings::getOption( 'commonsbooking_options_restrictions', 'restrictions-repair-body' );
 		$subject = Settings::getOption( 'commonsbooking_options_restrictions', 'restrictions-repair-subject', 'sanitize_text_field' );
 
@@ -96,7 +95,7 @@ protected function sendRepairMail() {
 	/**
 	 * Sends mail, when restriction is canceled (not active).
 	 */
-	protected function sendRestrictionCancelationMail() {
+	protected function sendRestrictionCancelationMail(): void {
 		$body    = Settings::getOption( 'commonsbooking_options_restrictions', 'restrictions-restriction-cancelled-body' );
 		$subject = Settings::getOption( 'commonsbooking_options_restrictions', 'restrictions-restriction-cancelled-subject', 'sanitize_text_field' );
 
@@ -116,7 +115,7 @@ protected function sendRestrictionCancelationMail() {
 	 *
 	 * @throws \Exception
 	 */
-	protected function prepareRestrictionMail( $body, $subject ) {
+	protected function prepareRestrictionMail( string $body, string $subject ): void {
 		$fromHeader  = 'From: ' . Settings::getOption( 'commonsbooking_options_restrictions', 'restrictions-from-name', 'sanitize_text_field' ) .
 						' <' . Settings::getOption( 'commonsbooking_options_restrictions', 'restrictions-from-email' ) . '>';
 		$restriction = $this->getRestriction();
diff --git a/src/Migration/Booking.php b/src/Migration/Booking.php
index 48947c2d9..7085dbaa4 100644
--- a/src/Migration/Booking.php
+++ b/src/Migration/Booking.php
@@ -8,8 +8,10 @@ class Booking {
 
 	/**
 	 * Changes post type of booking timeframes to cb_booking.
+	 *
+	 * @return int[]
 	 */
-	public static function migrate() {
+	public static function migrate(): array {
 
 		$bookings = Timeframe::getPostIdsByType(
 			[
diff --git a/src/Migration/Migration.php b/src/Migration/Migration.php
index fef012036..f5a253fdf 100644
--- a/src/Migration/Migration.php
+++ b/src/Migration/Migration.php
@@ -264,7 +264,7 @@ public static function migrateLocation( WP_Post $location ): bool {
 	 *
 	 * @param mixed $text
 	 *
-	 * @return array
+	 * @return array<int, string>
 	 */
 	public static function fetchEmails( $text ): array {
 		$words = str_word_count( $text, 1, '.@-_' );
@@ -278,11 +278,11 @@ function ( $word ) {
 	}
 
 	/**
-	 * @param $meta
+	 * @param array<string, array<int, mixed>> $meta
 	 *
-	 * @return array
+	 * @return array<string, mixed>
 	 */
-	private static function getFlatPostMeta( $meta ): array {
+	private static function getFlatPostMeta( array $meta ): array {
 		return array_map(
 			function ( $item ) {
 				return $item[0];
@@ -291,7 +291,12 @@ function ( $item ) {
 		);
 	}
 
-	private static function removeArrayItemsByKeys( $array, $keys ) {
+	/**
+	 * @param array<string, mixed> $array
+	 * @param string[] $keys
+	 * @return array<string, mixed>
+	 */
+	private static function removeArrayItemsByKeys( array $array, array $keys ): array {
 		foreach ( $keys as $ignoredMetaField ) {
 			if ( array_key_exists( $ignoredMetaField, $array ) ) {
 				unset( $array[ $ignoredMetaField ] );
@@ -302,15 +307,14 @@ private static function removeArrayItemsByKeys( $array, $keys ) {
 	}
 
 	/**
-	 * @param $id
-	 * @param $type
+	 * @param int $id
+	 * @param string $type
+	 * @param int|null $timeframe_type
 	 *
-	 * @param null $timeframe_type
-	 *
-	 * @return mixed
+	 * @return \WP_Post|null
 	 * @throws Exception
 	 */
-	public static function getExistingPost( $id, $type, $timeframe_type = null ) {
+	public static function getExistingPost( int $id, string $type, ?int $timeframe_type = null ): ?\WP_Post {
 		$args = array(
 			'meta_key'     => COMMONSBOOKING_METABOX_PREFIX . 'cb1_post_post_ID',
 			'meta_value'   => $id,
@@ -356,14 +360,14 @@ public static function getExistingPost( $id, $type, $timeframe_type = null ) {
 	}
 
 	/**
-	 * @param $existingPost
-	 * @param $postData array Post data
-	 * @param $postMeta array Post meta
+	 * @param \WP_Post|null $existingPost
+	 * @param array<string, mixed> $postData Post data
+	 * @param array<string, mixed> $postMeta Post meta
 	 *
 	 * @return bool
 	 * @throws \CommonsBooking\Geocoder\Exception\Exception
 	 */
-	protected static function savePostData( $existingPost, array $postData, array $postMeta ): bool {
+	protected static function savePostData( ?\WP_Post $existingPost, array $postData, array $postMeta ): bool {
 
 		$includeGeoData = array_key_exists( 'geodata', $_POST ) && sanitize_text_field( $_POST['geodata'] ) == 'true';
 
@@ -470,12 +474,12 @@ public static function migrateItem( WP_Post $item ): bool {
 	}
 
 	/**
-	 * @param $timeframe
+	 * @param array<string, mixed> $timeframe
 	 *
 	 * @return bool
 	 * @throws \CommonsBooking\Geocoder\Exception\Exception
 	 */
-	public static function migrateTimeframe( $timeframe ): bool {
+	public static function migrateTimeframe( array $timeframe ): bool {
 		$cbItem     = self::getExistingPost( $timeframe['item_id'], Item::$postType );
 		$cbLocation = self::getExistingPost( $timeframe['location_id'], Location::$postType );
 		$weekdays   = '';
@@ -522,13 +526,13 @@ public static function migrateTimeframe( $timeframe ): bool {
 	}
 
 	/**
-	 * @param $booking
+	 * @param array<string, mixed> $booking
 	 *
 	 * @return bool
 	 * @throws \CommonsBooking\Geocoder\Exception\Exception
 	 * @throws Exception
 	 */
-	public static function migrateBooking( $booking ): bool {
+	public static function migrateBooking( array $booking ): bool {
 		$user       = get_user_by( 'id', $booking['user_id'] );
 		$cbItem     = self::getExistingPost( $booking['item_id'], Item::$postType );
 		$cbLocation = self::getExistingPost( $booking['location_id'], Location::$postType );
@@ -573,11 +577,11 @@ public static function migrateBooking( $booking ): bool {
 	/**
 	 * Migrates CB1 Booking Code to CB2.
 	 *
-	 * @param $bookingCode
+	 * @param array<string, mixed> $bookingCode
 	 *
 	 * @return mixed
 	 */
-	public static function migrateBookingCode( $bookingCode ) {
+	public static function migrateBookingCode( array $bookingCode ) {
 		$cb2ItemId = CB1::getCB2ItemId( $bookingCode['item_id'] );
 		$date      = $bookingCode['booking_date'];
 		$code      = $bookingCode['bookingcode'];
@@ -606,7 +610,7 @@ public static function migrateUserAgreementUrl() {
 	/**
 	 * Migrates some of the CB1 Options that can be transfered to CB2
 	 */
-	public static function migrateCB1Options() {
+	public static function migrateCB1Options(): void {
 		// migrate Booking-Codes
 		$cb1_bookingcodes = Settings::getOption( 'commons-booking-settings-codes', 'commons-booking_codes_pool' );
 		Settings::updateOption( 'commonsbooking_options_bookingcodes', 'bookingcodes', $cb1_bookingcodes );
@@ -627,7 +631,7 @@ public static function migrateCB1Options() {
 	 *
 	 * @return void
 	 */
-	public static function migrateTaxonomy( $cb1Taxonomy ) {
+	public static function migrateTaxonomy( object $cb1Taxonomy ): void {
 		if ( $cb2PostId = CB1::getCB2PostIdByCB1Id( $cb1Taxonomy->object_id ) ) {
 			$terms = wp_get_object_terms( $cb1Taxonomy->object_id, $cb1Taxonomy->taxonomy );
 			$term  = array();
diff --git a/src/Model/BookablePost.php b/src/Model/BookablePost.php
index 6fd9e27bf..1a5f5e652 100644
--- a/src/Model/BookablePost.php
+++ b/src/Model/BookablePost.php
@@ -20,10 +20,10 @@ class BookablePost extends CustomPost {
 	 *
 	 * @uses Timeframe::getBookableForCurrentUser()
 	 *
-	 * @param bool        $asModel - Whether to return the timeframes as model (CommonsBooking\Model\Timeframe) or as array of WP_Post
-	 * @param array       $locations - If called from Item, this array should contain the location IDs to filter the timeframes
-	 * @param array       $items - If called from Location, this array should contain the item IDs to filter the timeframes
-	 * @param string|null $date - A datestring to get only the timeframes that are bookable on a specific date
+	 * @param bool                  $asModel - Whether to return the timeframes as model (CommonsBooking\Model\Timeframe) or as array of WP_Post
+	 * @param array<int, int>       $locations - If called from Item, this array should contain the location IDs to filter the timeframes
+	 * @param array<int, int>       $items - If called from Location, this array should contain the item IDs to filter the timeframes
+	 * @param string|null           $date - A datestring to get only the timeframes that are bookable on a specific date
 	 *
 	 * @return \CommonsBooking\Model\Timeframe[]|\WP_Post[] - An array of Timeframe models or WP_Post, an empty array if no bookable timeframes were found
 	 * @throws Exception
diff --git a/src/Model/Booking.php b/src/Model/Booking.php
index 8a5a4411c..75c278873 100755
--- a/src/Model/Booking.php
+++ b/src/Model/Booking.php
@@ -117,7 +117,7 @@ public function cancel(): void {
 	/**
 	 * Send mail to booking user, that it was canceled.
 	 */
-	protected function sendCancellationMail() {
+	protected function sendCancellationMail(): void {
 		$booking_msg = new BookingMessage( $this->getPost()->ID, 'canceled' );
 		$booking_msg->triggerMail();
 	}
@@ -162,8 +162,8 @@ public function showBookingCodes(): bool {
 	 * @throws Exception
 	 */
 	public function getBookableTimeFrame(): ?\CommonsBooking\Model\Timeframe {
-		$locationId = $this->getMeta( \CommonsBooking\Model\Timeframe::META_LOCATION_ID );
-		$itemId     = $this->getMeta( \CommonsBooking\Model\Timeframe::META_ITEM_ID );
+		$locationId = (int) $this->getMeta( \CommonsBooking\Model\Timeframe::META_LOCATION_ID );
+		$itemId     = (int) $this->getMeta( \CommonsBooking\Model\Timeframe::META_ITEM_ID );
 
 		$response = Timeframe::getBookable(
 			[ $locationId ],
@@ -186,7 +186,7 @@ public function getBookableTimeFrame(): ?\CommonsBooking\Model\Timeframe {
 	 *
 	 * @throws Exception
 	 */
-	public function assignBookableTimeframeFields() {
+	public function assignBookableTimeframeFields(): void {
 		$timeframe = $this->getBookableTimeFrame();
 		if ( $timeframe ) {
 			$neededMetaFields = [
@@ -273,7 +273,7 @@ private function adjacent( bool $previous = true ): ?Booking {
 	 *
 	 * @since 2.9.0
 	 *
-	 * @return array|null
+	 * @return array<int, Booking>|null
 	 * @throws Exception
 	 */
 	public function getAdjacentBookings(): ?array {
@@ -288,7 +288,7 @@ public function getAdjacentBookings(): ?array {
 	 * @since 2.9.0
 	 *
 	 * @param WP_User $user
-	 * @return array
+	 * @return array<int, Booking>
 	 */
 	public function getBookingChain( WP_User $user ): array {
 		$bookingChain    = [];
@@ -321,11 +321,11 @@ public function getBookingChain( WP_User $user ): array {
 	 * Returns time from repetition-[start/end] field in format H:i.
 	 * We need this meta-field in order to display the pick-up and return time to the user.
 	 *
-	 * @param $fieldName
+	 * @param string $fieldName
 	 *
 	 * @return string
 	 */
-	private function sanitizeTimeField( $fieldName ): string {
+	private function sanitizeTimeField( string $fieldName ): string {
 		$time       = Wordpress::getUTCDateTime();
 		$fieldValue = $this->getStartDate();
 		if ( $fieldName === 'end-time' ) {
@@ -747,7 +747,7 @@ public function isPast(): bool {
 	 *
 	 * @since 2.9.0
 	 *
-	 * @param int|array|string $term
+	 * @param int|array<int, int|string>|string $term
 	 * @return bool
 	 */
 	public function termsApply( $term ): bool {
@@ -974,9 +974,9 @@ public static function getTotalDuration( array $bookings ): int {
 	 *
 	 * @since 2.9.0
 	 *
-	 * @param Booking[]   $bookings The booking to check
-	 * @param array|false $terms The terms that the bookings are filtered against
-	 * @return array|null
+	 * @param Booking[]                        $bookings The booking to check
+	 * @param array<int, int|string>|false     $terms The terms that the bookings are filtered against
+	 * @return array<int, Booking>|null
 	 */
 	public static function filterTermsApply( array $bookings, $terms ): ?array {
 		if ( ! empty( $terms ) ) {
@@ -1000,9 +1000,9 @@ public static function filterTermsApply( array $bookings, $terms ): ?array {
 	 *
 	 * @since 2.9.0
 	 *
-	 * @param   array   $bookings
-	 * @param WP_User $user
-	 * @return array|null
+	 * @param array<int, Booking> $bookings
+	 * @param WP_User             $user
+	 * @return array<int, Booking>|null
 	 */
 	public static function filterForUser( array $bookings, WP_User $user ): ?array {
 		return array_filter(
diff --git a/src/Model/BookingCode.php b/src/Model/BookingCode.php
index da9adeb13..7db40e62b 100644
--- a/src/Model/BookingCode.php
+++ b/src/Model/BookingCode.php
@@ -43,11 +43,11 @@ class BookingCode {
 	/**
 	 * BookingCode constructor.
 	 *
-	 * @param $date
-	 * @param $item
-	 * @param $code
+	 * @param string $date
+	 * @param int $item
+	 * @param string $code
 	 */
-	public function __construct( $date, $item, $code ) {
+	public function __construct( string $date, int $item, string $code ) {
 		$this->date = $date;
 		$this->item = $item;
 		$this->code = $code;
@@ -67,7 +67,7 @@ public function getItem(): int {
 		return $this->item;
 	}
 
-	public function getItemName() {
+	public function getItemName(): string {
 		$post = get_post( $this->getItem() );
 
 		return $post->post_title;
diff --git a/src/Model/Calendar.php b/src/Model/Calendar.php
index 806b52feb..3bbe0360f 100644
--- a/src/Model/Calendar.php
+++ b/src/Model/Calendar.php
@@ -34,7 +34,7 @@ class Calendar {
 	protected array $locations;
 
 	/**
-	 * @var array
+	 * @var array<int|string, mixed>
 	 */
 	protected $types;
 
@@ -48,11 +48,11 @@ class Calendar {
 	/**
 	 * Calendar constructor.
 	 *
-	 * @param Day   $startDate
-	 * @param Day   $endDate
-	 * @param int[] $locations
-	 * @param int[] $items
-	 * @param array $types
+	 * @param Day                      $startDate
+	 * @param Day                      $endDate
+	 * @param int[]                    $locations
+	 * @param int[]                    $items
+	 * @param array<int|string, mixed> $types
 	 */
 	public function __construct( Day $startDate, Day $endDate, array $locations = [], array $items = [], array $types = [] ) {
 		// check, that it spans at least two days
@@ -82,7 +82,7 @@ public function __construct( Day $startDate, Day $endDate, array $locations = []
 	 *
 	 * Uses cache and expires at midnight on a daily basis.
 	 *
-	 * @return array
+	 * @return array<int, Week>
 	 */
 	public function getWeeks(): array {
 		$startDate = strtotime( $this->startDate->getDate() ) + 1;
@@ -102,8 +102,8 @@ public function getWeeks(): array {
 		} else {
 			$weeks = array();
 			while ( $startDate <= $endDate ) {
-				$dayOfYear = date( 'z', $startDate );
-				$year      = date( 'Y', $startDate );
+				$dayOfYear = (int) date( 'z', $startDate );
+				$year      = (int) date( 'Y', $startDate );
 				$weeks[]   = new Week(
 					$year,
 					$dayOfYear,
@@ -129,7 +129,7 @@ public function getWeeks(): array {
 	 * Because we process the calendar by weeks, at least two days are needed to get a valid calendar.
 	 * The calendar does not consider the individual boundaries set by $startDate and $endDate but will always return a full week.
 	 *
-	 * @return array
+	 * @return array<int, \stdClass>
 	 * @throws \Exception
 	 */
 	public function getAvailabilitySlots(): array {
diff --git a/src/Model/CustomPost.php b/src/Model/CustomPost.php
index ec47fd928..055a511d6 100644
--- a/src/Model/CustomPost.php
+++ b/src/Model/CustomPost.php
@@ -54,11 +54,11 @@ public function __construct( $post ) {
 	/**
 	 * Returns field value, even if it's a meta field.
 	 *
-	 * @param $fieldName
+	 * @param string $fieldName
 	 *
 	 * @return mixed
 	 */
-	public function getFieldValue( $fieldName ) {
+	public function getFieldValue( string $fieldName ) {
 		$fieldName  = trim( $fieldName );
 		$fieldValue = $this->{$fieldName};
 
@@ -74,9 +74,9 @@ public function getFieldValue( $fieldName ) {
 	 *
 	 * @param string $field key of post_meta field for this post
 	 *
-	 * @return string|array The value of the meta field. An empty string if the field doesn't exist.
+	 * @return string|array<mixed> The value of the meta field. An empty string if the field doesn't exist.
 	 */
-	public function getMeta( $field ) {
+	public function getMeta( string $field ) {
 		return get_post_meta( $this->post->ID, $field, true );
 	}
 
@@ -99,11 +99,11 @@ public function getMetaInt( string $key ): ?int {
 	 * When getting a value from a Model Object, we can use this magic method to get the value from the WP_Post object instead.
 	 * This, for example, allows us to use $booking->post_title instead of $booking->post->post_title.
 	 *
-	 * @param $name
+	 * @param string $name
 	 *
-	 * @return array|mixed|void
+	 * @return array<mixed>|mixed|void
 	 */
-	public function __get( $name ) {
+	public function __get( string $name ) {
 		if ( $this->post == null ) {
 			return;
 		}
@@ -116,13 +116,13 @@ public function __get( $name ) {
 	/**
 	 * Enables that we can call methods of \CustomPost as template tags.
 	 *
-	 * @param string $name of the member function
-	 * @param array  $arguments given to the template tag.
+	 * @param string       $name of the member function
+	 * @param array<mixed> $arguments given to the template tag.
 	 *
-	 * @return array|mixed|void
+	 * @return array<mixed>|mixed|void
 	 * @throws \ReflectionException if called template tag is not a registered method
 	 */
-	public function __call( $name, $arguments ) {
+	public function __call( string $name, array $arguments ) {
 		if ( method_exists( $this->post, $name ) ) {
 			$reflectionMethod = new ReflectionMethod( $this->post, $name );
 
diff --git a/src/Model/Day.php b/src/Model/Day.php
index 72d0ec13f..041f91403 100644
--- a/src/Model/Day.php
+++ b/src/Model/Day.php
@@ -23,17 +23,17 @@ class Day {
 	protected $date;
 
 	/**
-	 * @var array
+	 * @var array<int, int>
 	 */
 	protected $locations;
 
 	/**
-	 * @var array
+	 * @var array<int, int>
 	 */
 	protected $items;
 
 	/**
-	 * @var array|mixed
+	 * @var array<int|string, mixed>
 	 */
 	protected $types;
 
@@ -45,11 +45,11 @@ class Day {
 	/**
 	 * Day constructor.
 	 *
-	 * @param string $date
-	 * @param array  $locations
-	 * @param array  $items
-	 * @param array  $types
-	 * @param array  $possibleTimeframes
+	 * @param string                              $date
+	 * @param array<int, int|\WP_Post>            $locations
+	 * @param array<int, int|\WP_Post>            $items
+	 * @param array<int|string, mixed>            $types
+	 * @param array<int, \CommonsBooking\Model\Timeframe> $possibleTimeframes
 	 */
 	public function __construct( string $date, array $locations = [], array $items = [], array $types = [], array $possibleTimeframes = [] ) {
 		$this->date      = $date;
@@ -151,7 +151,7 @@ public function getTimeframes(): array {
 	/**
 	 * Returns array with restrictions.
 	 *
-	 * @return array
+	 * @return array<int, \CommonsBooking\Model\Restriction>
 	 * @throws Exception
 	 */
 	public function getRestrictions(): array {
@@ -169,7 +169,7 @@ public function getRestrictions(): array {
 	 * Returns grid for the day defined by the timeframes.
 	 *
 	 * @see Day::getTimeframeSlots()
-	 * @return array
+	 * @return array<int, array<string, mixed>>
 	 * @throws Exception
 	 */
 	public function getGrid(): array {
@@ -253,9 +253,9 @@ protected function getRestrictionStartSlot( int $grid, Restriction $restriction
 	/**
 	 * Returns end-slot id.
 	 *
-	 * @param array                           $slots
-	 * @param int                             $grid
-	 * @param \CommonsBooking\Model\Timeframe $timeframe
+	 * @param array<int, array<string, mixed>> $slots
+	 * @param int                              $grid
+	 * @param \CommonsBooking\Model\Timeframe  $timeframe
 	 *
 	 * @return float|int
 	 * @throws Exception
@@ -287,9 +287,9 @@ protected function getEndSlot( array $slots, int $grid, \CommonsBooking\Model\Ti
 	/**
 	 * Returns end slot for restriction.
 	 *
-	 * @param array       $slots
-	 * @param int         $grid
-	 * @param Restriction $restriction
+	 * @param array<int, array<string, mixed>> $slots
+	 * @param int                              $grid
+	 * @param Restriction                      $restriction
 	 *
 	 * @return float|int
 	 * @throws Exception
@@ -407,11 +407,12 @@ public function filterTimeframe( \CommonsBooking\Model\Timeframe $timeframe ): b
 	/**
 	 * Maps timeframes to timeslots.
 	 *
-	 * @param array $slots untyped structure of timeframe slot information
+	 * @param array<int, array<string, mixed>> $slots untyped structure of timeframe slot information
 	 *
+	 * @return void
 	 * @throws Exception
 	 */
-	protected function mapTimeFrames( array &$slots ) {
+	protected function mapTimeFrames( array &$slots ): void {
 		$grid = 24 / count( $slots );
 
 		// Iterate through timeframes and fill slots
@@ -440,11 +441,12 @@ protected function mapTimeFrames( array &$slots ) {
 	/**
 	 * Overwrites restricted slots
 	 *
-	 * @param array $slots
+	 * @param array<int, array<string, mixed>> $slots
 	 *
+	 * @return void
 	 * @throws Exception
 	 */
-	protected function mapRestrictions( array &$slots ) {
+	protected function mapRestrictions( array &$slots ): void {
 		$grid = 24 / count( $slots );
 
 		// Iterate through timeframes and fill slots
@@ -487,9 +489,11 @@ public function getEndTimestamp(): int {
 	/**
 	 * Remove empty and merge connected slots.
 	 *
-	 * @param array $slots Given an array of assocs in hourly slot resolution.
+	 * @param array<int, array<string, mixed>> $slots Given an array of assocs in hourly slot resolution.
+	 *
+	 * @return void
 	 */
-	protected function sanitizeSlots( array &$slots ) {
+	protected function sanitizeSlots( array &$slots ): void {
 		$this->removeEmptySlots( $slots );
 
 		// merge multiple slots if they are of same type
@@ -523,9 +527,11 @@ protected function sanitizeSlots( array &$slots ) {
 	/**
 	 * remove slots without timeframes
 	 *
-	 * @param $slots
+	 * @param array<int, array<string, mixed>> $slots
+	 *
+	 * @return void
 	 */
-	protected function removeEmptySlots( &$slots ) {
+	protected function removeEmptySlots( array &$slots ): void {
 		// remove slots without timeframes
 		foreach ( $slots as $slotNr => $slot ) {
 			if ( ! array_key_exists( 'timeframe', $slot ) || ! ( $slot['timeframe'] instanceof WP_Post ) ) {
@@ -541,7 +547,7 @@ protected function removeEmptySlots( &$slots ) {
 	 * Implementation note: An hourly resolution is used, but as a last step, the hourly slots are merged into
 	 * the representation that is configured in the timeframes.
 	 *
-	 * @return array
+	 * @return array<int, array<string, mixed>>
 	 * @throws Exception
 	 */
 	protected function getTimeframeSlots(): array {
@@ -582,24 +588,24 @@ protected function getTimeframeSlots(): array {
 	/**
 	 * Returns timestamp when $slotNr starts.
 	 *
-	 * @param $slotsPerDay
-	 * @param $slotNr
+	 * @param int $slotsPerDay
+	 * @param int $slotNr
 	 *
 	 * @return false|float|int
 	 */
-	protected function getSlotTimestampStart( $slotsPerDay, $slotNr ) {
+	protected function getSlotTimestampStart( int $slotsPerDay, int $slotNr ) {
 		return strtotime( $this->getDate() ) + ( $slotNr * ( ( 24 / $slotsPerDay ) * 3600 ) );
 	}
 
 	/**
 	 * Returns timestamp when $slotNr ends.
 	 *
-	 * @param $slotsPerDay
-	 * @param $slotNr
+	 * @param int $slotsPerDay
+	 * @param int $slotNr
 	 *
 	 * @return false|float|int
 	 */
-	protected function getSlotTimestampEnd( $slotsPerDay, $slotNr ) {
+	protected function getSlotTimestampEnd( int $slotsPerDay, int $slotNr ) {
 		return strtotime( $this->getDate() ) + ( ( $slotNr + 1 ) * ( ( 24 / $slotsPerDay ) * 3600 ) ) - 1;
 	}
 }
diff --git a/src/Model/Item.php b/src/Model/Item.php
index 25aeae158..87d7e69a0 100644
--- a/src/Model/Item.php
+++ b/src/Model/Item.php
@@ -18,14 +18,14 @@ class Item extends BookablePost {
 	/**
 	 * Returns all bookable timeframes for a specific location.
 	 *
-	 * @param $locationId
+	 * @param int  $locationId
 	 *
 	 * @param bool $asModel
 	 *
-	 * @return array
+	 * @return array<int, \CommonsBooking\Model\Timeframe>|\WP_Post[]
 	 * @throws Exception
 	 */
-	public function getBookableTimeframesByLocation( $locationId, bool $asModel = false ): array {
+	public function getBookableTimeframesByLocation( int $locationId, bool $asModel = false ): array {
 		return Timeframe::getBookableForCurrentUser(
 			[ $locationId ],
 			[ $this->ID ],
@@ -70,7 +70,7 @@ public function getAdmins() {
 	 *
 	 * This function is not used anywhere yet.
 	 *
-	 * @return array
+	 * @return array<int, \CommonsBooking\Model\Restriction>
 	 * @throws Exception
 	 */
 	public function getRestrictions(): array {
diff --git a/src/Model/Location.php b/src/Model/Location.php
index bc178aaf3..e5102ea0a 100644
--- a/src/Model/Location.php
+++ b/src/Model/Location.php
@@ -25,7 +25,7 @@ class Location extends BookablePost {
 	 * @param mixed $itemId
 	 * @param bool  $asModel
 	 *
-	 * @return array
+	 * @return array<int, \CommonsBooking\Model\Timeframe>|\WP_Post[]
 	 * @throws \Exception
 	 */
 	public function getBookableTimeframesByItem( $itemId, bool $asModel = false ): array {
@@ -187,7 +187,7 @@ public function formattedPickupInstructionsOneLine() {
 	 * Calls the geocoder to update the geo coordinates of the location.
 	 * Caution: Do not call this function without a one-second delay between calls. Do not overload the geocoder.
 	 */
-	public function updateGeoLocation() {
+	public function updateGeoLocation(): void {
 		$street        = $this->getMeta( COMMONSBOOKING_METABOX_PREFIX . 'location_street' );
 		$postCode      = $this->getMeta( COMMONSBOOKING_METABOX_PREFIX . 'location_postcode' );
 		$city          = $this->getMeta( COMMONSBOOKING_METABOX_PREFIX . 'location_city' );
diff --git a/src/Model/Map.php b/src/Model/Map.php
index e48253f64..cd0269419 100644
--- a/src/Model/Map.php
+++ b/src/Model/Map.php
@@ -19,9 +19,9 @@ class Map extends CustomPost {
 	 * attaches start / enddate of the bookable timeframe to the item
 	 * Fetches location & item metadata to be displayed on the map
 	 *
-	 * @param $mapItemTerms array of term ids
+	 * @param array<int, int> $mapItemTerms array of term ids
 	 *
-	 * @return array with postIDs as keys for an array with location data relevant for this map
+	 * @return array<int, array<string, mixed>> with postIDs as keys for an array with location data relevant for this map
 	 * @throws Exception
 	 */
 	public function get_locations( array $mapItemTerms ): array {
@@ -168,12 +168,12 @@ function ( $item ) {
 	/**
 	 * recursive clean up of location data entries
 	 *
-	 * @param $value
-	 * @param $linebreak_replacement
+	 * @param mixed  $value
+	 * @param string $linebreak_replacement
 	 *
 	 * @return mixed|string|string[]|null
 	 */
-	public static function cleanup_location_data_entry( $value, $linebreak_replacement ) {
+	public static function cleanup_location_data_entry( $value, string $linebreak_replacement ) {
 
 		if ( is_string( $value ) ) {
 			$value = wp_strip_all_tags( $value ); // strip all tags
@@ -193,12 +193,12 @@ public static function cleanup_location_data_entry( $value, $linebreak_replaceme
 	/**
 	 * clean up the location data
 	 *
-	 * @param $locations
-	 * @param $linebreak_replacement
+	 * @param array<int, array<string, mixed>> $locations
+	 * @param string                           $linebreak_replacement
 	 *
-	 * @return mixed
+	 * @return array<int, array<string, mixed>>
 	 */
-	public static function cleanup_location_data( $locations, $linebreak_replacement ) {
+	public static function cleanup_location_data( array $locations, string $linebreak_replacement ) {
 		foreach ( $locations as &$location ) {
 			$location = self::cleanup_location_data_entry( $location, $linebreak_replacement );
 		}
diff --git a/src/Model/Restriction.php b/src/Model/Restriction.php
index 80bd7cfbd..db3025237 100644
--- a/src/Model/Restriction.php
+++ b/src/Model/Restriction.php
@@ -81,8 +81,10 @@ class Restriction extends CustomPost {
 
 	const NO_END_TIMESTAMP = 3000000000;
 
+	/** @var bool|null */
 	protected $active;
 
+	/** @var bool|null */
 	protected $canceled;
 
 	/**
@@ -287,7 +289,7 @@ public function getLocationId() {
 	 * Apply restriction workflow.
 	 * Will cancel the bookings if restriction is active and type is total breakdown.
 	 */
-	public function apply() {
+	public function apply(): void {
 		// Check if this is an active restriction
 		if ( $this->isActive() ) {
 			$bookings = \CommonsBooking\Repository\Booking::getByRestriction( $this );
@@ -334,7 +336,7 @@ public function getType() {
 	 * TODO:
 	 *      Duplicated implementation in Model/Timeframe.php
 	 *
-	 * @return array
+	 * @return array<int, int>
 	 */
 	public function getAdmins() {
 
@@ -377,7 +379,7 @@ public function getAdmins() {
 	 *
 	 * @param Booking[] $bookings booking post objects.
 	 */
-	protected function cancelBookings( $bookings ) {
+	protected function cancelBookings( array $bookings ): void {
 		foreach ( $bookings as $booking ) {
 			$booking->cancel();
 		}
@@ -391,7 +393,7 @@ protected function cancelBookings( $bookings ) {
 	 *
 	 * @param Booking[] $bookings booking post objects.
 	 */
-	protected function sendRestrictionMails( $bookings ) {
+	protected function sendRestrictionMails( array $bookings ): void {
 		foreach ( $bookings as $key => $booking ) {
 			// get User ID from booking
 			$userId = $booking->getUserData()->ID;
diff --git a/src/Model/Timeframe.php b/src/Model/Timeframe.php
index 6b135ce72..2cae5992c 100644
--- a/src/Model/Timeframe.php
+++ b/src/Model/Timeframe.php
@@ -206,8 +206,10 @@ public function isUserPrivileged( \WP_User $user ): bool {
 			return true;
 		}
 
-		$itemAdmin     = commonsbooking_isUserAllowedToEdit( $this->getItem(), $user );
-		$locationAdmin = commonsbooking_isUserAllowedToEdit( $this->getLocation(), $user );
+		$item          = $this->getItem();
+		$location      = $this->getLocation();
+		$itemAdmin     = $item ? commonsbooking_isUserAllowedToEdit( $item->ID, $user ) : false;
+		$locationAdmin = $location ? commonsbooking_isUserAllowedToEdit( $location->ID, $user ) : false;
 		return ( $itemAdmin || $locationAdmin );
 	}
 
@@ -855,12 +857,12 @@ public function overlaps( Timeframe $otherTimeframe ): bool {
 	/**
 	 * Checks if timeframes are overlapping in weekly slot and slot with manual repetition.
 	 *
-	 * @param $weeklyTimeframe
-	 * @param $manualTimeframe
+	 * @param Timeframe $weeklyTimeframe
+	 * @param Timeframe $manualTimeframe
 	 *
 	 * @return bool
 	 */
-	private static function hasWeeklyManualOverlap( $weeklyTimeframe, $manualTimeframe ): bool {
+	private static function hasWeeklyManualOverlap( Timeframe $weeklyTimeframe, Timeframe $manualTimeframe ): bool {
 		$manualSelectionWeekdays = array_unique(
 			array_map(
 				fn ( $date ) => date( 'w', strtotime( $date ) ),
diff --git a/src/Model/Week.php b/src/Model/Week.php
index 41ddad092..f34bde020 100644
--- a/src/Model/Week.php
+++ b/src/Model/Week.php
@@ -27,19 +27,19 @@ class Week {
 	protected $dayOfYear;
 
 	/**
-	 * @var array
+	 * @var int[]
 	 */
-	protected $locations;
+	protected array $locations;
 
 	/**
-	 * @var array
+	 * @var int[]
 	 */
-	protected $items;
+	protected array $items;
 
 	/**
-	 * @var array
+	 * @var string[]
 	 */
-	protected $types;
+	protected array $types;
 
 	/**
 	 * @var Timeframe[]
@@ -49,14 +49,14 @@ class Week {
 	/**
 	 * Week constructor.
 	 *
-	 * @param $year
-	 * @param $dayOfYear
-	 * @param array       $locations
-	 * @param array       $items
-	 * @param array       $types
+	 * @param int $year
+	 * @param int $dayOfYear
+	 * @param int[] $locations
+	 * @param int[] $items
+	 * @param string[] $types
 	 * @param Timeframe[] $possibleTimeframes Timeframes that might be relevant for this week, need to be filtered.
 	 */
-	public function __construct( $year, $dayOfYear, array $locations = [], array $items = [], array $types = [], array $possibleTimeframes = [] ) {
+	public function __construct( int $year, int $dayOfYear, array $locations = [], array $items = [], array $types = [], array $possibleTimeframes = [] ) {
 		if ( $year === null ) {
 			$year = date( 'Y' );
 		}
@@ -76,7 +76,7 @@ public function __construct( $year, $dayOfYear, array $locations = [], array $it
 	 *
 	 * Uses the cache and expires at midnight on a daily basis.
 	 *
-	 * @return array
+	 * @return \CommonsBooking\Model\Day[]
 	 * @throws Exception
 	 */
 	public function getDays() {
diff --git a/src/Plugin.php b/src/Plugin.php
index b7e143506..308263720 100644
--- a/src/Plugin.php
+++ b/src/Plugin.php
@@ -47,7 +47,7 @@ class Plugin {
 	/**
 	 * Plugin activation tasks.
 	 */
-	public static function activation() {
+	public static function activation(): void {
 		// Register custom user roles (e.g. cb_manager)
 		self::addCustomUserRoles();
 
@@ -63,7 +63,7 @@ public static function activation() {
 	/**
 	 * Plugin deactivation tasks.
 	 */
-	public static function deactivation() {
+	public static function deactivation(): void {
 		do_action( Scheduler::UNSCHEDULER_HOOK );
 	}
 
@@ -108,7 +108,7 @@ public static function addCPTRoleCaps() {
 	 *
 	 * @return bool[][]
 	 */
-	public static function getRoleCapMapping( $roleName = null ) {
+	public static function getRoleCapMapping( ?string $roleName = null ) {
 		if ( $roleName === null ) {
 			return [
 				// We deliberately don't use the getManagerRoles from the UserRepository here, because the custom roles should be able to define their own permissions
@@ -133,7 +133,7 @@ public static function getRoleCapMapping( $roleName = null ) {
 	/**
 	 * Adds cb user roles to WordPress.
 	 */
-	public static function addCustomUserRoles() {
+	public static function addCustomUserRoles(): void {
 		foreach ( self::getRoleCapMapping() as $roleName => $caps ) {
 			$role = get_role( $roleName );
 			if ( ! $role ) {
@@ -250,7 +250,7 @@ public static function getManagedDepsVersions(): ?array {
 	 *
 	 * @return bool
 	 */
-	public static function isPostCustomPostType( $post ): bool {
+	public static function isPostCustomPostType( int|\WP_Post $post ): bool {
 		if ( is_int( $post ) ) {
 			$post = get_post( $post );
 		}
@@ -281,9 +281,10 @@ private static function getCBManagerCustomPostTypeClasses(): array {
 	/**
 	 * Adds permissions to edit custom post types for specified role.
 	 *
-	 * @param $postType
+	 * @param string $postType
+	 * @param string $roleName
 	 */
-	protected static function addRoleCaps( $postType, $roleName ) {
+	protected static function addRoleCaps( string $postType, string $roleName ): void {
 		// Add the roles you'd like to administer the custom post types
 		$roles = array_keys( self::getRoleCapMapping( $roleName ) );
 
@@ -322,7 +323,7 @@ protected static function addRoleCaps( $postType, $roleName ) {
 		}
 	}
 
-	public static function admin_init() {
+	public static function admin_init(): void {
 		// check if we have a new version and run tasks
 		Upgrade::runTasksAfterUpdate();
 
@@ -341,7 +342,7 @@ public static function admin_init() {
 	/**
 	 * Adds menu pages.
 	 */
-	public static function addMenuPages() {
+	public static function addMenuPages(): void {
 		// Dashboard
 		add_menu_page(
 			'Commons Booking',
@@ -470,7 +471,7 @@ public static function filterAdminBodyClass( $classes ) {
 	/**
 	 * Registers custom post types.
 	 */
-	public static function registerCustomPostTypes() {
+	public static function registerCustomPostTypes(): void {
 		foreach ( self::getCustomPostTypeObjects() as $customPostType ) {
 			$cptArgs = $customPostType->getArgs();
 			// make export possible when using WP_DEBUG, this allows us to use the export feature for creating new E2E tests
@@ -486,7 +487,7 @@ public static function registerCustomPostTypes() {
 	/**
 	 * Registers additional post statuses.
 	 */
-	public static function registerPostStates() {
+	public static function registerPostStates(): void {
 		foreach ( Booking::$bookingStates as $bookingState ) {
 			new PostStatus( $bookingState, __( ucfirst( $bookingState ), 'commonsbooking' ) );
 		}
@@ -496,7 +497,7 @@ public static function registerPostStates() {
 	 * Renders error for backend_notice.
 	 * TODO refactor this using the AdminMessage type
 	 */
-	public static function renderError() {
+	public static function renderError(): void {
 		$errorTypes = [
 			Model\Timeframe::ERROR_TYPE,
 			Model\Timeframe::ORPHANED_TYPE,
@@ -537,7 +538,7 @@ public static function renderError() {
 	/**
 	 * Enable Legacy CB1 profile fields.
 	 */
-	public static function maybeEnableCB1UserFields() {
+	public static function maybeEnableCB1UserFields(): void {
 		$enabled = Settings::getOption( 'commonsbooking_options_migration', 'enable-cb1-user-fields' );
 		if ( $enabled == 'on' ) {
 			new CB1UserFields();
@@ -547,7 +548,7 @@ public static function maybeEnableCB1UserFields() {
 	/**
 	 * Register Admin-Options
 	 */
-	public static function registerAdminOptions() {
+	public static function registerAdminOptions(): void {
 		$options_array = include COMMONSBOOKING_PLUGIN_DIR . '/includes/OptionsArray.php';
 		foreach ( $options_array as $tab_id => $tab ) {
 			new OptionsTab( $tab_id, $tab );
@@ -567,7 +568,7 @@ private static function packagedVersion( string $key ): string {
 		return $versions[ $key ] ?? '0';
 	}
 
-	public static function registerScriptsAndStyles() {
+	public static function registerScriptsAndStyles(): void {
 		$base = COMMONSBOOKING_PLUGIN_ASSETS_URL . 'packaged/';
 
 		// spin.js
@@ -704,18 +705,18 @@ public static function registerScriptsAndStyles() {
 		);
 	}
 
-	public function registerShortcodes() {
+	public function registerShortcodes(): void {
 		add_shortcode( 'cb_search', array( SearchShortcode::class, 'execute' ) );
 	}
 
 	/**
 	 * Registers all user data exporters ({@link https://developer.wordpress.org/plugins/privacy/adding-the-personal-data-exporter-to-your-plugin/}).
 	 *
-	 * @param array $exporters
+	 * @param array<string, array<string, mixed>> $exporters
 	 *
-	 * @return mixed
+	 * @return array<string, array<string, mixed>>
 	 */
-	public static function registerUserDataExporters( $exporters ) {
+	public static function registerUserDataExporters( array $exporters ): array {
 		$exporters[ COMMONSBOOKING_PLUGIN_SLUG ] = array(
 			'exporter_friendly_name' => __( 'CommonsBooking Bookings', 'commonsbooking' ),
 			'callback'               => array( \CommonsBooking\Wordpress\CustomPostType\Booking::class, 'exportUserBookingsByEmail' ),
@@ -726,11 +727,11 @@ public static function registerUserDataExporters( $exporters ) {
 	/**
 	 * Registers all user data erasers ({@link https://developer.wordpress.org/plugins/privacy/adding-the-personal-data-eraser-to-your-plugin/}).
 	 *
-	 * @param $erasers
+	 * @param array<string, array<string, mixed>> $erasers
 	 *
-	 * @return mixed
+	 * @return array<string, array<string, mixed>>
 	 */
-	public static function registerUserDataErasers( $erasers ) {
+	public static function registerUserDataErasers( array $erasers ): array {
 		$erasers[ COMMONSBOOKING_PLUGIN_SLUG ] = array(
 			'eraser_friendly_name' => __( 'CommonsBooking Bookings', 'commonsbooking' ),
 			'callback'             => array( \CommonsBooking\Wordpress\CustomPostType\Booking::class, 'removeUserBookingsByEmail' ),
@@ -741,7 +742,7 @@ public static function registerUserDataErasers( $erasers ) {
 	/**
 	 *  Init hooks.
 	 */
-	public function init() {
+	public function init(): void {
 		do_action( 'cmb2_init' );
 
 		// Enable CB1 User Fields (needed in case of migration from cb 0.9.x)
@@ -860,13 +861,13 @@ public function commonsbooking_load_textdomain() {
 	 *
 	 * @TODO: Add test if cache is cleared correctly.
 	 *
-	 * @param $post_id
-	 * @param $post
-	 * @param $update
+	 * @param int      $post_id
+	 * @param \WP_Post $post
+	 * @param bool     $update
 	 *
 	 * @throws \CommonsBooking\Psr\Cache\InvalidArgumentException
 	 */
-	public function savePostActions( $post_id, $post, $update ) {
+	public function savePostActions( int $post_id, \WP_Post $post, bool $update ): void {
 		if ( ! self::isPostCustomPostType( $post ) ) {
 			return;
 		}
@@ -880,7 +881,7 @@ public function savePostActions( $post_id, $post, $update ) {
 	}
 
 	/**
-	 * @return array
+	 * @return string[]
 	 */
 	public static function getCustomPostTypesLabels(): array {
 		return [
@@ -899,11 +900,11 @@ public static function getCustomPostTypesLabels(): array {
 	/**
 	 * Function to register our new routes from the controller.
 	 */
-	public function initRoutes() {
+	public function initRoutes(): void {
 		// Check if API is activated in settings
 		$api_activated = Settings::getOption( 'commonsbooking_options_api', 'api-activated' );
 		if ( $api_activated != 'on' ) {
-			return false;
+			return;
 		}
 
 		add_action(
@@ -937,7 +938,7 @@ function () {
 	 * - Hook appropriate function to button that sends out emails with booking codes to the station.
 	 *   @see \CommonsBooking\View\BookingCodes::renderDirectEmailRow()
 	 */
-	public function initBookingcodes() {
+	public function initBookingcodes(): void {
 		add_action( 'admin_action_cb_download-bookingscodes-csv', array( View\BookingCodes::class, 'renderCSV' ), 10, 0 );
 		add_action( 'admin_action_cb_email-bookingcodes', array( View\BookingCodes::class, 'emailCodes' ), 10, 0 );
 	}
@@ -949,7 +950,7 @@ public function initBookingcodes() {
 	 *
 	 * @return string
 	 */
-	public function setParentFile( $parent_file ): string {
+	public function setParentFile( string $parent_file ): string {
 		global $current_screen;
 
 		// Set 'cb-dashboard' as parent for cb post types
@@ -986,7 +987,7 @@ public function setParentFile( $parent_file ): string {
 	 *
 	 * @return string
 	 */
-	public function getTheContent( $content ): string {
+	public function getTheContent( string $content ): string {
 		// Check if we're inside the main loop in a single post page.
 		if ( is_single() && in_the_loop() && is_main_query() ) {
 			global $post;
@@ -1000,12 +1001,12 @@ public function getTheContent( $content ): string {
 		return $content;
 	}
 
-	public function registerUserWidget() {
+	public function registerUserWidget(): void {
 		register_widget( '\CommonsBooking\Wordpress\Widget\UserWidget' );
 	}
 
 
-	function AddImageSizes() {
+	function AddImageSizes(): void {
 
 		$crop = Settings::getOption( 'commonsbooking_options_templates', 'image_listing_crop' ) == 'on' ? true : false;
 
diff --git a/src/Repository/BookablePost.php b/src/Repository/BookablePost.php
index 924eed4a6..3a8e5bd7d 100644
--- a/src/Repository/BookablePost.php
+++ b/src/Repository/BookablePost.php
@@ -29,7 +29,7 @@ abstract class BookablePost extends PostRepository {
 	 *
 	 * @param bool $publishedOnly
 	 *
-	 * @return array
+	 * @return WP_Post[]
 	 * @throws CacheException
 	 * @throws InvalidArgumentException
 	 */
@@ -153,7 +153,7 @@ abstract protected static function getTaxonomyName();
 	 * @param mixed $userId
 	 * @param bool  $asModel - Whether the posts should be returned as their respective model class or as WP_Post
 	 *
-	 * @return array
+	 * @return WP_Post[]|object[]
 	 */
 	public static function getByUserId( $userId, bool $asModel = false ): array {
 		$cbPosts = [];
@@ -214,12 +214,12 @@ abstract protected static function getModelClass();
 	/**
 	 * Returns an array of CB item post objects
 	 *
-	 * @param array $args WP Post args
-	 * @param bool  $bookable
+	 * @param array<string, mixed> $args WP Post args
+	 * @param bool                 $bookable
 	 *
-	 * @return array
+	 * @return object[]
 	 */
-	public static function get( array $args = array(), bool $bookable = false ) {
+	public static function get( array $args = array(), bool $bookable = false ): array {
 		$posts             = [];
 		$args['post_type'] = static::getPostType();
 		$args['nopaging']  = true;
@@ -268,15 +268,15 @@ public static function get( array $args = array(), bool $bookable = false ) {
 	 * Returns related object based on bookable post.
 	 * Example: We'd like to have the items bookable at a specific location. With this function we are able to get them.
 	 *
-	 * @param $postId
-	 * @param $originType
-	 * @param $relatedType
-	 * @param bool $bookable
+	 * @param int|WP_Post $postId
+	 * @param string      $originType
+	 * @param string      $relatedType
+	 * @param bool        $bookable
 	 *
-	 * @return int[] Array of post ids
+	 * @return WP_Post[]|object[] Array of post objects
 	 * @throws Exception
 	 */
-	protected static function getByRelatedPost( $postId, $originType, $relatedType, bool $bookable = false ): array {
+	protected static function getByRelatedPost( int|WP_Post $postId, string $originType, string $relatedType, bool $bookable = false ): array {
 
 		if ( ! in_array( $originType, self::$relationalTypes ) || ! in_array( $relatedType, self::$relationalTypes ) ) {
 			throw new Exception( 'invalid type submitted' );
@@ -316,13 +316,13 @@ protected static function getByRelatedPost( $postId, $originType, $relatedType,
 	 * Returns array with related posts for post with post id and origin type.
 	 * Works only for locations and items!
 	 *
-	 * @param $postId
-	 * @param $originType
-	 * @param $relatedType
+	 * @param int|WP_Post $postId
+	 * @param string $originType
+	 * @param string $relatedType
 	 *
-	 * @return array
+	 * @return array<int, mixed>
 	 */
-	protected static function getRelatedPosts( $postId, $originType, $relatedType ): array {
+	protected static function getRelatedPosts( $postId, string $originType, string $relatedType ): array {
 		if ( $postId instanceof WP_Post ) {
 			$postId = $postId->ID;
 		}
diff --git a/src/Repository/Booking.php b/src/Repository/Booking.php
index 2fb725d54..30c9179a5 100644
--- a/src/Repository/Booking.php
+++ b/src/Repository/Booking.php
@@ -15,30 +15,30 @@ class Booking extends PostRepository {
 	/**
 	 * Returns 0:00 timestamp for day of $timestamp.
 	 *
-	 * @param $timestamp
+	 * @param int $timestamp
 	 *
 	 * @return false|int
 	 */
-	protected static function getStartTimestamp( $timestamp ) {
+	protected static function getStartTimestamp( int $timestamp ) {
 		return strtotime( 'midnight', $timestamp );
 	}
 
 	/**
 	 * Returns 23:59 timestamp for day of $timestamp.
 	 *
-	 * @param $startTimestamp
+	 * @param int $startTimestamp
 	 *
 	 * @return false|int
 	 */
-	protected static function getEndTimestamp( $startTimestamp ) {
+	protected static function getEndTimestamp( int $startTimestamp ) {
 		return strtotime( '+23 Hours +59 Minutes +59 Seconds', $startTimestamp );
 	}
 
 	/**
 	 * Returns bookings ending at day of timestamp.
 	 *
-	 * @param int   $timestamp
-	 * @param array $customArgs
+	 * @param int                  $timestamp
+	 * @param array<string, mixed> $customArgs
 	 *
 	 * @return \CommonsBooking\Model\Booking[]
 	 * @throws Exception
@@ -83,8 +83,8 @@ public static function getEndingBookingsByDate( int $timestamp, array $customArg
 	/**
 	 * Returns bookings beginning at day of timestamp.
 	 *
-	 * @param int   $timestamp
-	 * @param array $customArgs
+	 * @param int                  $timestamp
+	 * @param array<string, mixed> $customArgs
 	 *
 	 * @return \CommonsBooking\Model\Booking[]
 	 * @throws Exception
@@ -209,12 +209,12 @@ function ( $post ) {
 	}
 
 	/**
-	 * @param int   $startDate
-	 * @param int   $endDate
-	 * @param $locationId
-	 * @param $itemId
-	 * @param array $customArgs
-	 * @param array $postStatus
+	 * @param int                  $startDate
+	 * @param int                  $endDate
+	 * @param int|null             $locationId
+	 * @param int|null             $itemId
+	 * @param array<string, mixed> $customArgs
+	 * @param string[]             $postStatus
 	 *
 	 * @return \CommonsBooking\Model\Booking[]
 	 * @throws Exception
@@ -222,8 +222,8 @@ function ( $post ) {
 	public static function getByTimerange(
 		int $startDate,
 		int $endDate,
-		$locationId = null,
-		$itemId = null,
+		?int $locationId = null,
+		?int $itemId = null,
 		array $customArgs = [],
 		array $postStatus = [ 'confirmed', 'unconfirmed' ]
 	): array {
@@ -279,8 +279,10 @@ public static function getByTimerange(
 	/**
 	 * Returns all bookings, allowed to see for user.
 	 *
+	 * @param \WP_User $user
 	 * @param bool     $asModel if true, returns as Booking array, if false, return int array (defaults to false)
 	 * @param int|null $minTimestamp
+	 * @param string[] $postStatus
 	 *
 	 * @return \CommonsBooking\Model\Booking[]|int[]
 	 * @throws Exception
@@ -288,7 +290,7 @@ public static function getByTimerange(
 	public static function getForUser(
 		\WP_User $user,
 		bool $asModel = false,
-		$minTimestamp = null,
+		?int $minTimestamp = null,
 		array $postStatus = [ 'canceled', 'confirmed', 'unconfirmed' ]
 	): array {
 		$customId  = $user->ID;
@@ -327,16 +329,17 @@ function ( $post ) use ( $user ) {
 	/**
 	 * Returns all bookings, allowed to see/edit for current user.
 	 *
-	 * @param bool $asModel
-	 * @param null $startDate
+	 * @param bool     $asModel
+	 * @param int|null $startDate
+	 * @param string[] $postStatus
 	 *
-	 * @return array
+	 * @return \CommonsBooking\Model\Booking[]|int[]
 	 * @throws Exception
 	 */
 	public static function getForCurrentUser(
 		bool $asModel = false,
-		$startDate = null,
-		$postStatus = [ 'canceled', 'confirmed', 'unconfirmed' ]
+		?int $startDate = null,
+		array $postStatus = [ 'canceled', 'confirmed', 'unconfirmed' ]
 	): array {
 		if ( ! is_user_logged_in() ) {
 			return [];
@@ -351,12 +354,12 @@ public static function getForCurrentUser(
 	 * Returns bookings. This uses the CommonsBooking\Repository\Timeframe::get() method which
 	 * is not based on the WP_Query class but will perform its own SQL query.
 	 *
-	 * @param array       $locations
-	 * @param array       $items
+	 * @param int[]       $locations
+	 * @param int[]       $items
 	 * @param string|null $date Date-String in format YYYY-mm-dd
 	 * @param bool        $returnAsModel if true, returns booking model, if false return int array (defaults to false)
 	 * @param int|null    $minTimestamp
-	 * @param array       $postStatus
+	 * @param string[]    $postStatus
 	 *
 	 * @return int[]|\CommonsBooking\Model\Booking[]
 	 * @throws Exception
@@ -385,10 +388,11 @@ public static function get(
 	 * This is to prevent timeouts for bigger queries such as data exports. As opposed to the getForUser() function,
 	 * this function will use the WP_Query class to perform the query allowing us to use the pagination features of WP_Query.
 	 *
-	 * @param \WP_User $user The user for which to get the bookings.
-	 * @param int      $page The current page that is processed.
-	 * @param int      $perPage The number of bookings per page. A lower number will result in faster queries.
-	 * @param array    $customArgs Valid WP_Query args array.
+	 * @param \WP_User             $user The user for which to get the bookings.
+	 * @param int                  $page The current page that is processed.
+	 * @param int                  $perPage The number of bookings per page. A lower number will result in faster queries.
+	 * @param array<string, mixed> $customArgs Valid WP_Query args array.
+	 * @param string[]             $postStatus
 	 *
 	 * @return \CommonsBooking\Model\Booking[] An array of Booking models.
 	 */
@@ -396,8 +400,8 @@ public static function getForUserPaginated(
 		\WP_User $user,
 		int $page = 1,
 		int $perPage = 10,
-		$customArgs = [],
-		$postStatus = [ 'confirmed', 'unconfirmed', 'canceled', 'publish', 'inherit' ]
+		array $customArgs = [],
+		array $postStatus = [ 'confirmed', 'unconfirmed', 'canceled', 'publish', 'inherit' ]
 	): array {
 		$args = array(
 			'author'         => $user->ID,
@@ -445,15 +449,15 @@ public static function getByRestriction( \CommonsBooking\Model\Restriction $rest
 	 * This is used to check if the given parameters are overlapping with existing bookings.
 	 * The given $postID will be excluded from the result so that the given booking will not be counted as overlapping.
 	 *
-	 * @param $itemId
-	 * @param $locationId
+	 * @param int      $itemId
+	 * @param int      $locationId
 	 * @param int      $startDate
 	 * @param int      $endDate
 	 * @param int|null $postId
 	 *
 	 * @return \CommonsBooking\Model\Booking[] empty array if none are found
 	 */
-	public static function getExistingBookings( $itemId, $locationId, $startDate, $endDate, $postId = null ): array {
+	public static function getExistingBookings( int $itemId, int $locationId, int $startDate, int $endDate, ?int $postId = null ): array {
 
 		// Get existing bookings for defined parameters
 		$existingBookingsInRange = self::getByTimerange(
@@ -477,7 +481,7 @@ public static function getExistingBookings( $itemId, $locationId, $startDate, $e
 	/**
 	 * Will take a valid WP_Query args array and return an array of Booking models.
 	 *
-	 * @param array $args
+	 * @param array<string, mixed> $args
 	 *
 	 * @return \CommonsBooking\Model\Booking[]
 	 * @throws Exception
diff --git a/src/Repository/BookingCodes.php b/src/Repository/BookingCodes.php
index dd61efed9..68f5ebf44 100644
--- a/src/Repository/BookingCodes.php
+++ b/src/Repository/BookingCodes.php
@@ -41,7 +41,7 @@ class BookingCodes {
 	 * @param int|null $endDate - Where to get booking codes to (timestamp)
 	 * @param int      $advanceGenerationDays - Open-ended timeframes: If 0, generate code(s) until today. If >0, generate additional codes after today
 	 *
-	 * @return array
+	 * @return array<int, BookingCode>
 	 * @throws BookingCodeException
 	 */
 	public static function getCodes( int $timeframeId, ?int $startDate = null, ?int $endDate = null, int $advanceGenerationDays = self::ADVANCE_GENERATION_DAYS ): array {
@@ -142,7 +142,7 @@ public static function getCodes( int $timeframeId, ?int $startDate = null, ?int
 	 *
 	 * @return void works by reference on param $bookingCodes
 	 */
-	private static function backwardCompatibilityFilter( &$bookingCodes, $preferredTimeframeId, $preferredLocationId ) {
+	private static function backwardCompatibilityFilter( mixed &$bookingCodes, int $preferredTimeframeId, int $preferredLocationId ): void {
 		$filteredCodes = [];
 		$codesByDate   = [];
 
@@ -415,7 +415,7 @@ public static function persist( BookingCode $bookingCode, $timeframeId = 0, $loc
 	/**
 	 * Will get the configured booking codes from the settings and return them as an array.
 	 *
-	 * @return array - Array of booking codes, empty array if no booking codes are configured.
+	 * @return array<int, string> Array of booking codes, empty array if no booking codes are configured.
 	 */
 	private static function getCodesArray(): array {
 		$bookingCodes = Settings::getOption( 'commonsbooking_options_bookingcodes', 'bookingcodes' );
diff --git a/src/Repository/CB1.php b/src/Repository/CB1.php
index 0b519ada2..4681587af 100644
--- a/src/Repository/CB1.php
+++ b/src/Repository/CB1.php
@@ -56,18 +56,18 @@ public static function isInstalled() {
 	/**
 	 * Get the old CB1 location post type posts
 	 *
-	 * @return array
+	 * @return \WP_Post[]
 	 */
-	public static function getLocations() {
+	public static function getLocations(): array {
 		return self::get( self::$LOCATION_TYPE_ID );
 	}
 
 	/**
-	 * @param $postType
+	 * @param string $postType
 	 *
-	 * @return array
+	 * @return \WP_Post[]
 	 */
-	protected static function get( $postType ) {
+	protected static function get( string $postType ): array {
 		$posts = [];
 		$args  = array(
 			'post_type'   => $postType,
@@ -85,9 +85,9 @@ protected static function get( $postType ) {
 	/**
 	 * Get the old CB1 item post type posts
 	 *
-	 * @return array
+	 * @return \WP_Post[]
 	 */
-	public static function getItems() {
+	public static function getItems(): array {
 		return self::get( self::$ITEM_TYPE_ID );
 	}
 
@@ -148,7 +148,7 @@ public static function getBookingCodes() {
 	 *
 	 * @return ?string
 	 */
-	public static function getBookingCode( $id ): ?string {
+	public static function getBookingCode( int $id ): ?string {
 		global $wpdb;
 		$table_bookingcodes = $wpdb->prefix . self::$BOOKINGCODES_TABLE;
 
@@ -209,7 +209,7 @@ protected static function getCB2PostIdByType( int $id, string $type ) {
 	 *
 	 * @return false|int
 	 */
-	public static function getCB2ItemId( $locationId ) {
+	public static function getCB2ItemId( int $locationId ): int|false {
 		return self::getCB2PostIdByType( $locationId, \CommonsBooking\Wordpress\CustomPostType\Item::$postType );
 	}
 
@@ -218,7 +218,7 @@ public static function getCB2ItemId( $locationId ) {
 	 *
 	 * @return false|int
 	 */
-	public static function getCB2TimeframeId( $timeframeId ) {
+	public static function getCB2TimeframeId( int $timeframeId ): int|false {
 		return self::getCB2PostIdByType( $timeframeId, \CommonsBooking\Wordpress\CustomPostType\Timeframe::$postType );
 	}
 
@@ -229,7 +229,7 @@ public static function getCB2TimeframeId( $timeframeId ) {
 	 *
 	 * @return ?int
 	 */
-	public static function getCB2PostIdByCB1Id( $id ): ?int {
+	public static function getCB2PostIdByCB1Id( int $id ): ?int {
 		global $wpdb;
 		$table_postmeta = $wpdb->prefix . 'postmeta';
 
diff --git a/src/Repository/Item.php b/src/Repository/Item.php
index ada54a228..dabd5c25e 100644
--- a/src/Repository/Item.php
+++ b/src/Repository/Item.php
@@ -9,14 +9,13 @@ class Item extends BookablePost {
 	/**
 	 * Returns array with items at location based on bookable timeframes.
 	 *
-	 * @param $locationId
-	 *
+	 * @param int $locationId
 	 * @param bool $bookable
 	 *
-	 * @return array
+	 * @return array<int, mixed>
 	 * @throws Exception
 	 */
-	public static function getByLocation( $locationId, bool $bookable = false ): array {
+	public static function getByLocation( int $locationId, bool $bookable = false ): array {
 		return self::getByRelatedPost( $locationId, 'location', 'item', $bookable );
 	}
 
diff --git a/src/Repository/Location.php b/src/Repository/Location.php
index ae3b881c1..e8198681e 100644
--- a/src/Repository/Location.php
+++ b/src/Repository/Location.php
@@ -9,14 +9,13 @@ class Location extends BookablePost {
 	/**
 	 * Returns array with locations for item based on bookable timeframes.
 	 *
-	 * @param $itemId
-	 *
+	 * @param int $itemId
 	 * @param bool $bookable
 	 *
-	 * @return array
+	 * @return array<int, mixed>
 	 * @throws Exception
 	 */
-	public static function getByItem( $itemId, bool $bookable = false ): array {
+	public static function getByItem( int $itemId, bool $bookable = false ): array {
 		return self::getByRelatedPost( $itemId, 'item', 'location', $bookable );
 	}
 
diff --git a/src/Repository/PostRepository.php b/src/Repository/PostRepository.php
index 16135751a..96e27493d 100644
--- a/src/Repository/PostRepository.php
+++ b/src/Repository/PostRepository.php
@@ -18,7 +18,7 @@ abstract class PostRepository {
 	 * @throws \CommonsBooking\Psr\Cache\CacheException
 	 * @throws \CommonsBooking\Psr\Cache\InvalidArgumentException
 	 */
-	public static function getPostById( $postId ) {
+	public static function getPostById( int $postId ) {
 		$cacheItem = Plugin::getCacheItem();
 		if ( $cacheItem ) {
 			return $cacheItem;
diff --git a/src/Repository/Restriction.php b/src/Repository/Restriction.php
index 38cc197db..3d75d699f 100644
--- a/src/Repository/Restriction.php
+++ b/src/Repository/Restriction.php
@@ -12,11 +12,11 @@ class Restriction extends PostRepository {
 	/**
 	 * Returns active restrictions.
 	 *
-	 * @param array       $locations one or more location ids to filter
-	 * @param array       $items     one or more item ids to filter
+	 * @param int[]       $locations one or more location ids to filter
+	 * @param int[]       $items     one or more item ids to filter
 	 * @param string|null $date if provided, filters restrictions to be valid on the given date
 	 * @param bool        $returnAsModel returns array of models instead of ids, default false (returns ids)
-	 * @param int         $minTimestamp if provided, returns restrictions where rep-end > min-timestamp. default null
+	 * @param int|null    $minTimestamp if provided, returns restrictions where rep-end > min-timestamp. default null
 	 * @param string[]    $postStatus filters for given list of status, defaults to all WordPress post status enums
 	 *
 	 * @return \CommonsBooking\Model\Restriction[]
@@ -27,7 +27,7 @@ public static function get(
 		array $items = [],
 		?string $date = null,
 		bool $returnAsModel = false,
-		$minTimestamp = null,
+		?int $minTimestamp = null,
 		array $postStatus = [ 'confirmed', 'unconfirmed', 'publish', 'inherit' ]
 	): array {
 		$customCacheKey = serialize( $postStatus );
@@ -38,7 +38,7 @@ public static function get(
 		} else {
 			$posts = self::queryPosts( $date, $minTimestamp, $postStatus );
 
-			if ( $posts && count( $posts ) ) {
+			if ( $posts ) {
 				$posts = Wordpress::flattenWpdbResult( $posts );
 
 				// If there are locations or items to be filtered, we iterate through
@@ -64,13 +64,13 @@ public static function get(
 	 * Queries restriction posts from db.
 	 * Only queries active restrictions.
 	 *
-	 * @param $date
-	 * @param $minTimestamp int checks if rep-end > minTimestamp (0:00)
-	 * @param $postStatus
+	 * @param string|null $date
+	 * @param int|null    $minTimestamp checks if rep-end > minTimestamp (0:00)
+	 * @param string[]    $postStatus
 	 *
-	 * @return array|object|null
+	 * @return \WP_Post[]
 	 */
-	private static function queryPosts( $date, $minTimestamp, $postStatus ) {
+	private static function queryPosts( ?string $date, ?int $minTimestamp, array $postStatus ): array {
 		$cacheItem = Plugin::getCacheItem();
 		if ( $cacheItem ) {
 			return $cacheItem;
@@ -109,11 +109,11 @@ private static function queryPosts( $date, $minTimestamp, $postStatus ) {
 	/**
 	 * Returns filter to query be minimum timestamp.
 	 *
-	 * @param $minTimestamp
+	 * @param int $minTimestamp
 	 *
 	 * @return string
 	 */
-	private static function getMinTimestampQuery( $minTimestamp ): string {
+	private static function getMinTimestampQuery( int $minTimestamp ): string {
 		global $wpdb;
 		$table_postmeta = $wpdb->prefix . 'postmeta';
 
@@ -141,11 +141,11 @@ private static function getMinTimestampQuery( $minTimestamp ): string {
 	/**
 	 * Returns query to filter by date.
 	 *
-	 * @param $date
+	 * @param string $date
 	 *
 	 * @return string
 	 */
-	private static function getDateQuery( $date ): string {
+	private static function getDateQuery( string $date ): string {
 		global $wpdb;
 		$table_postmeta = $wpdb->prefix . 'postmeta';
 
@@ -196,11 +196,11 @@ private static function getActiveQuery(): string {
 	 * WARNING: This method will filter out posts that are only queried by item OR location.
 	 * Meaning, if a restriction is created that has a location and an item, but the query only contains the location, the restriction will not be returned.
 	 *
-	 * @param array $posts
-	 * @param array $locations
-	 * @param array $items
+	 * @param \WP_Post[] $posts
+	 * @param int[]      $locations
+	 * @param int[]      $items
 	 *
-	 * @return array
+	 * @return \WP_Post[]
 	 */
 	private static function filterPosts( array $posts, array $locations, array $items ): array {
 		return array_filter(
@@ -251,12 +251,12 @@ function ( $post ) use ( $locations, $items ) {
 	/**
 	 * Casts all posts in the array to Restriction objects.
 	 *
-	 * @param $posts
+	 * @param \WP_Post[] $posts
 	 *
-	 * @return mixed
+	 * @return \CommonsBooking\Model\Restriction[]
 	 * @throws Exception
 	 */
-	private static function castPostsToRestrictions( $posts ) {
+	private static function castPostsToRestrictions( array $posts ): array {
 		foreach ( $posts as &$post ) {
 			$post = new \CommonsBooking\Model\Restriction( $post );
 		}
diff --git a/src/Repository/Timeframe.php b/src/Repository/Timeframe.php
index 3130c26c5..080a5cad7 100644
--- a/src/Repository/Timeframe.php
+++ b/src/Repository/Timeframe.php
@@ -19,14 +19,14 @@ class Timeframe extends PostRepository {
 	/**
 	 * Returns only bookable timeframes.
 	 *
-	 * @param array       $locations
-	 * @param array       $items
+	 * @param int[]       $locations
+	 * @param int[]       $items
 	 * @param string|null $date
 	 * @param bool        $returnAsModel
-	 * @param $minTimestamp
-	 * @param array       $postStatus
+	 * @param int|null    $minTimestamp
+	 * @param string[]    $postStatus
 	 *
-	 * @return array
+	 * @return int[]|\WP_Post[]|\CommonsBooking\Model\Timeframe[]|\CommonsBooking\Model\Booking[]
 	 * @throws Exception
 	 */
 	public static function getBookable(
@@ -34,7 +34,7 @@ public static function getBookable(
 		array $items = [],
 		?string $date = null,
 		bool $returnAsModel = false,
-		$minTimestamp = null,
+		?int $minTimestamp = null,
 		array $postStatus = [ 'confirmed', 'unconfirmed', 'publish', 'inherit' ]
 	): array {
 		return self::get(
@@ -51,14 +51,14 @@ public static function getBookable(
 	/**
 	 * Returns only bookable timeframes for current user.
 	 *
-	 * @param array       $locations
-	 * @param array       $items
+	 * @param int[]       $locations
+	 * @param int[]       $items
 	 * @param string|null $date
 	 * @param bool        $returnAsModel
-	 * @param $minTimestamp
-	 * @param array       $postStatus
+	 * @param int|null    $minTimestamp
+	 * @param string[]    $postStatus
 	 *
-	 * @return array
+	 * @return int[]|\WP_Post[]|\CommonsBooking\Model\Timeframe[]|\CommonsBooking\Model\Booking[]
 	 * @throws Exception
 	 */
 	public static function getBookableForCurrentUser(
@@ -66,7 +66,7 @@ public static function getBookableForCurrentUser(
 		array $items = [],
 		?string $date = null,
 		bool $returnAsModel = false,
-		$minTimestamp = null,
+		?int $minTimestamp = null,
 		array $postStatus = [ 'confirmed', 'unconfirmed', 'publish', 'inherit' ]
 	): array {
 
@@ -93,9 +93,9 @@ public static function getBookableForCurrentUser(
 	 * TODO: Investigate
 	 *       This function is not based on the WP_Query class, probably because of performance reasons.
 	 *
-	 * @param array       $locations
-	 * @param array       $items
-	 * @param array       $types
+	 * @param int[]       $locations
+	 * @param int[]       $items
+	 * @param int[]       $types
 	 * @param string|null $date Date-String in format YYYY-mm-dd
 	 * @param bool        $returnAsModel if true, returns as custom wp-post model, if false, return wp-post or int array (defaults to false)
 	 * @param int|null    $minTimestamp
@@ -165,9 +165,9 @@ public static function get(
 	/**
 	 * Will get all timeframes in the database to perform mass operations on (like migrations).
 	 *
-	 * @param int   $page
-	 * @param int   $perPage
-	 * @param array $customArgs
+	 * @param int                  $page
+	 * @param int                  $perPage
+	 * @param array<string, mixed> $customArgs
 	 *
 	 * @return \stdClass Properties: array posts, int totalPosts, int totalPages, bool done
 	 * @throws Exception
@@ -218,15 +218,16 @@ public static function getAllPaginated(
 	 * We need this for the Timeframe Export, so that it does not time out on large datasets.
 	 * This function is in general slower than the getInRange function. But it can be used in AJAX requests.
 	 *
-	 * @param int      $minTimestamp
-	 * @param int|null $maxTimestamp
-	 * @param int      $page
-	 * @param int      $perPage
-	 * @param array    $types
-	 * @param bool     $asModel
-	 * @param array    $customArgs
-	 *
-	 * @return array An array with the keys 'posts', 'totalPages' and 'done' (bool) to indicate if there are more posts to fetch
+	 * @param int                  $minTimestamp
+	 * @param int|null             $maxTimestamp
+	 * @param int                  $page
+	 * @param int                  $perPage
+	 * @param int[]                $types
+	 * @param string[]             $postStatus
+	 * @param bool                 $asModel
+	 * @param array<string, mixed> $customArgs
+	 *
+	 * @return array<string, mixed> An array with the keys 'posts', 'totalPages' and 'done' (bool) to indicate if there are more posts to fetch
 	 */
 	public static function getInRangePaginated(
 		int $minTimestamp,
@@ -240,7 +241,7 @@ public static function getInRangePaginated(
 			\CommonsBooking\Wordpress\CustomPostType\Timeframe::REPAIR_ID,
 			\CommonsBooking\Wordpress\CustomPostType\Timeframe::OFF_HOLIDAYS_ID,
 		],
-		$postStatus = [ 'confirmed', 'unconfirmed', 'canceled', 'publish', 'inherit' ],
+		array $postStatus = [ 'confirmed', 'unconfirmed', 'canceled', 'publish', 'inherit' ],
 		bool $asModel = false,
 		array $customArgs = []
 	): array {
@@ -323,9 +324,9 @@ function ( $post ) use ( $args ) {
 	 *
 	 * Why? It's because of performance. We use the ids as base set for following filter queries.
 	 *
-	 * @param array $types the types of timeframes to return, will return default set when not set
-	 * @param array $items the items that the timeframes should be applicable to, will return all if not set
-	 * @param array $locations the locations that the timeframes should be applicable to, will return all if not set
+	 * @param int[] $types the types of timeframes to return, will return default set when not set
+	 * @param int[] $items the items that the timeframes should be applicable to, will return all if not set
+	 * @param int[] $locations the locations that the timeframes should be applicable to, will return all if not set
 	 *
 	 * @since 2.9.0 Supports now single and multi selection for items and locations
 	 *
@@ -425,6 +426,12 @@ function ( $post ) {
 	 *
 	 * @since 2.9.0 Supports now single and multi selection for items and locations
 	 *
+	 * @param string   $joinAlias
+	 * @param string   $table_postmeta
+	 * @param int[]    $entities
+	 * @param string   $singleEntityKey
+	 * @param string   $multiEntityKey
+	 *
 	 * @return string join statement
 	 */
 	private static function getEntityQuery( string $joinAlias, string $table_postmeta, array $entities, string $singleEntityKey, string $multiEntityKey ): string {
@@ -457,13 +464,13 @@ private static function getEntityQuery( string $joinAlias, string $table_postmet
 	 * Queries for posts within $postIds and filters them by $date and/or $minTimestamp and $postStatus.
 	 * Why? This kind of filtering is needed nearly everywhere in commonsbooking.
 	 *
-	 * @param string|null $date
-	 * @param int|null    $minTimestamp
-	 * @param int|null    $maxTimestamp
-	 * @param array       $postIds
-	 * @param array       $postStatus
+	 * @param string|null    $date
+	 * @param int|null       $minTimestamp
+	 * @param int|null       $maxTimestamp
+	 * @param string[]|int[] $postIds
+	 * @param string[]       $postStatus
 	 *
-	 * @return array
+	 * @return \WP_Post[]
 	 */
 	private static function getPostsByBaseParams( ?string $date, ?int $minTimestamp, ?int $maxTimestamp, array $postIds, array $postStatus ): array {
 		$cacheItem = Plugin::getCacheItem();
@@ -624,10 +631,10 @@ private static function getTimerangeQuery( string $table_postmeta, int $minTimes
 	/**
 	 * Wrapper function for all filters.
 	 *
-	 * @param array       $posts
+	 * @param \WP_Post[]  $posts
 	 * @param string|null $date
 	 *
-	 * @return array
+	 * @return \WP_Post[]
 	 */
 	private static function filterTimeframes( array $posts, ?string $date ): array {
 		// Filter by configured days
@@ -642,10 +649,10 @@ private static function filterTimeframes( array $posts, ?string $date ): array {
 	 * Why? Because you can define days for your timeframe. Here's the point where we make sure, that only these days
 	 *      are taken into account.
 	 *
-	 * @param array       $posts
+	 * @param \WP_Post[]  $posts
 	 * @param string|null $date string format: YYYY-mm-dd
 	 *
-	 * @return array
+	 * @return \WP_Post[]
 	 * @throws \CommonsBooking\Psr\Cache\InvalidArgumentException
 	 */
 	private static function filterTimeframesByConfiguredDays( array $posts, ?string $date ): array {
@@ -681,11 +688,11 @@ function ( $post ) use ( $date ) {
 	 * Filters timeframes from array, which aren't bookable because of the max booking days in
 	 * advance setting.
 	 *
-	 * @param $posts
+	 * @param \WP_Post[] $posts
 	 *
-	 * @return array
+	 * @return \WP_Post[]
 	 */
-	private static function filterTimeframesByMaxBookingDays( $posts ): array {
+	private static function filterTimeframesByMaxBookingDays( array $posts ): array {
 		return array_filter(
 			$posts,
 			function ( $post ) {
@@ -710,11 +717,11 @@ function ( $post ) {
 	 * Filters timeframes from array,
 	 * removes timeframes which are not bookable by current user
 	 *
-	 * @param $posts
+	 * @param \WP_Post[]|\CommonsBooking\Model\Timeframe[]|\CommonsBooking\Model\Booking[] $posts
 	 *
-	 * @return array
+	 * @return \WP_Post[]|\CommonsBooking\Model\Timeframe[]|\CommonsBooking\Model\Booking[]
 	 */
-	private static function filterTimeframesForCurrentUser( $posts ): array {
+	private static function filterTimeframesForCurrentUser( array $posts ): array {
 		return array_filter(
 			$posts,
 			function ( $post ) {
@@ -768,9 +775,10 @@ function ( $timeframe ) use ( $startTimestamp, $endTimestamp ) {
 	 *
 	 * @param int[]|\WP_Post[] $posts
 	 *
+	 * @return void
 	 * @throws Exception
 	 */
-	private static function castPostsToModels( &$posts ) {
+	private static function castPostsToModels( array &$posts ): void {
 		foreach ( $posts as &$post ) {
 			// If we have a standard timeframe
 			if ( $post->post_type == \CommonsBooking\Wordpress\CustomPostType\Timeframe::getPostType() ) {
@@ -833,20 +841,20 @@ public static function getByLocationItemTimestamp( int $locationId, int $itemId,
 	 * Why? We often need timeframes for a specific timerange. For example in the calendar the default range is
 	 *      three months. Another example is the table view.
 	 *
-	 * @param $minTimestamp
-	 * @param $maxTimestamp
+	 * @param int      $minTimestamp
+	 * @param int      $maxTimestamp
 	 * @param int[]    $locations
 	 * @param int[]    $items
-	 * @param array    $types
+	 * @param int[]    $types
 	 * @param bool     $returnAsModel
 	 * @param string[] $postStatus
 	 *
-	 * @return array
+	 * @return int[]|\WP_Post[]|\CommonsBooking\Model\Timeframe[]|\CommonsBooking\Model\Booking[]
 	 * @throws Exception
 	 */
 	public static function getInRange(
-		$minTimestamp,
-		$maxTimestamp,
+		int $minTimestamp,
+		int $maxTimestamp,
 		array $locations = [],
 		array $items = [],
 		array $types = [],
@@ -903,20 +911,20 @@ public static function getInRange(
 	/**
 	 * Returns timeframes in explicit timerange that are bookable by the current user.
 	 *
-	 * @param $minTimestamp
-	 * @param $maxTimestamp
+	 * @param int      $minTimestamp
+	 * @param int      $maxTimestamp
 	 * @param int[]    $locations
 	 * @param int[]    $items
-	 * @param array    $types
+	 * @param int[]    $types
 	 * @param bool     $returnAsModel
 	 * @param string[] $postStatus
 	 *
-	 * @return array
+	 * @return int[]|\WP_Post[]|\CommonsBooking\Model\Timeframe[]|\CommonsBooking\Model\Booking[]
 	 * @throws Exception
 	 */
 	public static function getInRangeForCurrentUser(
-		$minTimestamp,
-		$maxTimestamp,
+		int $minTimestamp,
+		int $maxTimestamp,
 		array $locations = [],
 		array $items = [],
 		array $types = [],
diff --git a/src/Repository/UserRepository.php b/src/Repository/UserRepository.php
index b486617e0..3bfa95b79 100644
--- a/src/Repository/UserRepository.php
+++ b/src/Repository/UserRepository.php
@@ -90,7 +90,7 @@ public static function getOwners(): array {
 	/**
 	 * Returns an array of all User Roles as roleID => translated role name
 	 *
-	 * @return array
+	 * @return array<string, string>
 	 */
 	public static function getUserRoles(): array {
 		global $wp_roles;
@@ -115,8 +115,8 @@ public static function getUserRoles(): array {
 	 *
 	 * @since 2.9.0
 	 *
-	 * @param int          $userID
-	 * @param string|array $roles
+	 * @param int               $userID
+	 * @param string|string[]   $roles
 	 * @return bool
 	 */
 	public static function userHasRoles( int $userID, $roles ): bool {
diff --git a/src/Service/Booking.php b/src/Service/Booking.php
index 40c64c31b..7410f73b7 100644
--- a/src/Service/Booking.php
+++ b/src/Service/Booking.php
@@ -40,7 +40,7 @@ public static function cleanupBookings() {
 		}
 	}
 
-	private static function sendMessagesForDay( int $tsDate, bool $onStartDate, Message $message ) {
+	private static function sendMessagesForDay( int $tsDate, bool $onStartDate, Message $message ): void {
 		if ( $onStartDate ) {
 			$bookings = \CommonsBooking\Repository\Booking::getBeginningBookingsByDate( $tsDate );
 		} else {
@@ -63,7 +63,7 @@ private static function sendMessagesForDay( int $tsDate, bool $onStartDate, Mess
 	 *
 	 * @throws \Exception
 	 */
-	public static function sendReminderMessage() {
+	public static function sendReminderMessage(): void {
 
 		if ( Settings::getOption( 'commonsbooking_options_reminder', 'pre-booking-reminder-activate' ) != 'on' ) {
 			return;
@@ -80,7 +80,7 @@ public static function sendReminderMessage() {
 	 *
 	 * @throws \Exception
 	 */
-	public static function sendFeedbackMessage() {
+	public static function sendFeedbackMessage(): void {
 
 		if ( Settings::getOption( 'commonsbooking_options_reminder', 'post-booking-notice-activate' ) != 'on' ) {
 			return;
@@ -92,15 +92,15 @@ public static function sendFeedbackMessage() {
 		self::sendMessagesForDay( $endDate, false, $message );
 	}
 
-	public static function sendBookingStartLocationReminderMessage() {
+	public static function sendBookingStartLocationReminderMessage(): void {
 		self::sendLocationBookingReminderMessage( 'start' );
 	}
 
-	public static function sendBookingEndLocationReminderMessage() {
+	public static function sendBookingEndLocationReminderMessage(): void {
 		self::sendLocationBookingReminderMessage( 'end' );
 	}
 
-	protected static function sendLocationBookingReminderMessage( string $type ) {
+	protected static function sendLocationBookingReminderMessage( string $type ): void {
 
 		if ( Settings::getOption( 'commonsbooking_options_reminder', 'booking-' . $type . '-location-reminder-activate' ) != 'on' ) {
 			return;
diff --git a/src/Service/BookingCodes.php b/src/Service/BookingCodes.php
index 612b61151..bb0b3581c 100644
--- a/src/Service/BookingCodes.php
+++ b/src/Service/BookingCodes.php
@@ -58,7 +58,7 @@ public static function sendBookingCodesMessage(): void {
 	 *
 	 * @param int $timeframeId
 	 *
-	 * @return array|false   Parameters.
+	 * @return array{from: int, to: int, nextCronEventTs: int}|false   Parameters.
 	 */
 	public static function getCronParams( $timeframeId ) {
 		$tsCurrentCronEvent = get_post_meta( $timeframeId, \CommonsBooking\View\BookingCodes::NEXT_CRON_EMAIL, true );
diff --git a/src/Service/BookingRule.php b/src/Service/BookingRule.php
index bbe26f427..bd3aaf8d6 100644
--- a/src/Service/BookingRule.php
+++ b/src/Service/BookingRule.php
@@ -56,13 +56,13 @@ class BookingRule {
 	 * Array of associative arrays in which the key "title" is the title of the parameter and "description" is the description of the parameter.
 	 * These parameters are text fields that can be used to configure the rule. We can currently only support 2 parameters
 	 *
-	 * @var array
+	 * @var array<int, array<string, string>>
 	 */
 	protected array $params = [];
 	/**
 	 * Array where first element is the description of the select field and the second element is an associative array of the select options
 	 *
-	 * @var array
+	 * @var array<int, mixed>
 	 */
 	protected array $selectParam;
 	/**
@@ -81,8 +81,8 @@ class BookingRule {
 	 * @param String  $description A detailed description of the rule, will be shown to the configuration admin
 	 * @param String  $errorMessage The static error message that will be shown to the booking user if the rule is not met
 	 * @param Closure $validationFunction The function that will be called to validate the rule. This is a closure that takes a Booking object, the passed args and an array of the selected terms as arguments
-	 * @param array   $params Array of associative arrays in which the key "title" is the title of the parameter and "description" is the description of the parameter. Only 2 parameters are currently supported. They have to be integer values.
-	 * @param array   $selectParam Array where first element is the description of the select field and the second element is an associative array of the select options
+	 * @param array<int, array<string, string>>   $params Array of associative arrays in which the key "title" is the title of the parameter and "description" is the description of the parameter. Only 2 parameters are currently supported. They have to be integer values.
+	 * @param array<int, mixed>   $selectParam Array where first element is the description of the select field and the second element is an associative array of the select options
 	 *
 	 * @throws BookingRuleException
 	 */
@@ -126,7 +126,10 @@ public function getDescription(): string {
 	 *
 	 * @return string
 	 */
-	public function getErrorMessage( $args = [] ): string {
+	/**
+	 * @param array<int, mixed> $args
+	 */
+	public function getErrorMessage( array $args = [] ): string {
 		$errorMessage = commonsbooking_sanitizeHTML( $this->errorMessage );
 		if ( $this->errorFromArgs !== null ) {
 			$errorMessageFunction = $this->errorFromArgs;
@@ -145,7 +148,7 @@ public function getName(): string {
 	}
 
 	/**
-	 * @return array
+	 * @return array<int, array<string, string>>
 	 */
 	public function getParams(): array {
 		return $this->params;
@@ -161,7 +164,7 @@ public function getValidationFunction(): Closure {
 	/**
 	 * Create associative array for CMB2 select
 	 *
-	 * @return array
+	 * @return array<string, string>
 	 */
 	public static function getRulesForSelect(): array {
 		$assoc_array = [];
@@ -344,11 +347,11 @@ public static function init(): array {
 	 * If the user has bookings at the same day it will return an array with conflicting bookings
 	 * If there is no booking at the same day, will return null
 	 *
-	 * @param Booking    $booking
-	 * @param array      $args
-	 * @param bool|array $appliedTerms
+	 * @param Booking         $booking
+	 * @param array<int, mixed> $args
+	 * @param bool|array<mixed> $appliedTerms
 	 *
-	 * @return array|null
+	 * @return array<int, Booking>|null
 	 * @throws Exception
 	 */
 	public static function checkSimultaneousBookings( Booking $booking, array $args = [], $appliedTerms = false ): ?array {
@@ -371,11 +374,11 @@ function ( $userBooking ) use ( $booking ) {
 	 * If the user has chained too many days in that timespan will return the conflicting bookings
 	 * If the user bookings are NOT above the limit, will return null
 	 *
-	 * @param Booking    $booking
-	 * @param array      $args
-	 * @param bool|array $appliedTerms
+	 * @param Booking           $booking
+	 * @param array<int, mixed> $args
+	 * @param bool|array<mixed> $appliedTerms
 	 *
-	 * @return array|null
+	 * @return array<int, Booking>|null
 	 * @throws Exception
 	 */
 	public static function checkChainBooking( Booking $booking, array $args = [], $appliedTerms = false ): ?array {
@@ -432,11 +435,11 @@ function ( Booking $collectionItem ) use ( $booking ) {
 	 * Params: $args[0} = The amount of days the user is allowed to book
 	 *         $args[1] = The period over which the user is allowed to book
 	 *
-	 * @param Booking    $booking
-	 * @param array      $args
-	 * @param bool|array $appliedTerms
+	 * @param Booking           $booking
+	 * @param array<int, mixed> $args
+	 * @param bool|array<mixed> $appliedTerms
 	 *
-	 * @return array
+	 * @return array<int, Booking>|null
 	 * @throws Exception
 	 */
 	public static function checkMaxBookingDays( Booking $booking, array $args, $appliedTerms = false ): ?array {
@@ -456,7 +459,12 @@ public static function checkMaxBookingDays( Booking $booking, array $args, $appl
 		return self::checkBookingRangeForDays( $startOfPeriod, $endOfPeriod, $booking, $appliedTerms, $allowedBookedDays );
 	}
 
-	public static function maxBookingDaysErrorMessage( $args ) {
+	/**
+	 * @param array<int, mixed> $args
+	 *
+	 * @return string
+	 */
+	public static function maxBookingDaysErrorMessage( array $args ): string {
 		$allowedBookedDays = $args[0];
 		$periodDays        = $args[1];
 
@@ -472,11 +480,11 @@ public static function maxBookingDaysErrorMessage( $args ) {
 	 *         $args[1] : Unused
 	 *         $args[2]:  The day on which the counter is reset, default: 1 = sunday, 2 = monday, ..., 7 = saturday
 	 *
-	 * @param Booking    $booking
-	 * @param array      $args
-	 * @param bool|array $appliedTerms
+	 * @param Booking           $booking
+	 * @param array<int, mixed> $args
+	 * @param bool|array<mixed> $appliedTerms
 	 *
-	 * @return array|null
+	 * @return array<int, Booking>|null
 	 */
 	public static function checkMaxBookingDaysPerWeek( Booking $booking, array $args, $appliedTerms = false ): ?array {
 		$allowedBookableDays = $args[0];
@@ -487,6 +495,11 @@ public static function checkMaxBookingDaysPerWeek( Booking $booking, array $args
 		return self::checkBookingRangeForDays( $range[0], $range[1], $booking, $appliedTerms, $allowedBookableDays );
 	}
 
+	/**
+	 * @param array<int, mixed> $args
+	 *
+	 * @return string
+	 */
 	public static function maxDaysWeekErrorMessage( array $args ): string {
 		$maxDays        = $args[0];
 		$resetDay       = $args[2] - 1;
@@ -497,6 +510,13 @@ public static function maxDaysWeekErrorMessage( array $args ): string {
 		return sprintf( __( 'You can only book %1$s days per week, please try again after %2$s next week.', 'commonsbooking' ), $maxDays, $resetDayString );
 	}
 
+	/**
+	 * @param Booking           $booking
+	 * @param array<int, mixed> $args
+	 * @param bool|array<mixed> $appliedTerms
+	 *
+	 * @return array<int, Booking>|null
+	 */
 	public static function checkMaxBookingsWeek( Booking $booking, array $args, $appliedTerms = false ): ?array {
 		$allowedTotalBookings = $args[0];
 		// default is sunday
@@ -506,6 +526,11 @@ public static function checkMaxBookingsWeek( Booking $booking, array $args, $app
 		return self::checkBookingAmount( $range[0], $range[1], $booking, $appliedTerms, $allowedTotalBookings );
 	}
 
+	/**
+	 * @param array<int, mixed> $args
+	 *
+	 * @return string
+	 */
 	public static function maxBookingsWeekErrorMessage( array $args ): string {
 		$maxDays        = $args[0];
 		$resetDay       = $args[2];
@@ -524,11 +549,11 @@ public static function maxBookingsWeekErrorMessage( array $args ): string {
 	 *           $args[1] : Unused
 	 *         $args[2]:  The day on which the counter is reset, from 0 to max 31.
 	 *
-	 * @param Booking    $booking
-	 * @param array      $args
-	 * @param bool|array $appliedTerms
+	 * @param Booking           $booking
+	 * @param array<int, mixed> $args
+	 * @param bool|array<mixed> $appliedTerms
 	 *
-	 * @return array|null
+	 * @return array<int, Booking>|null
 	 */
 	public static function checkMaxBookingDaysPerMonth( Booking $booking, array $args, $appliedTerms = false ): ?array {
 		$allowedBookableDays = $args[0];
@@ -538,6 +563,11 @@ public static function checkMaxBookingDaysPerMonth( Booking $booking, array $arg
 		return self::checkBookingRangeForDays( $range[0], $range[1], $booking, $appliedTerms, $allowedBookableDays );
 	}
 
+	/**
+	 * @param array<int, mixed> $args
+	 *
+	 * @return string
+	 */
 	public static function maxDaysMonthErrorMessage( array $args ): string {
 		$maxDays  = $args[0];
 		$resetDay = $args[2];
@@ -546,6 +576,13 @@ public static function maxDaysMonthErrorMessage( array $args ): string {
 		return sprintf( __( 'You can only book %1$s days per month, please try again after the %2$s. next month.', 'commonsbooking' ), $maxDays, $resetDay );
 	}
 
+	/**
+	 * @param Booking           $booking
+	 * @param array<int, mixed> $args
+	 * @param bool|array<mixed> $appliedTerms
+	 *
+	 * @return array<int, Booking>|null
+	 */
 	public static function checkMaxBookingsMonth( Booking $booking, array $args, $appliedTerms = false ): ?array {
 		$allowedTotalBookings = $args[0];
 		$resetDay             = $args[2];
@@ -554,6 +591,11 @@ public static function checkMaxBookingsMonth( Booking $booking, array $args, $ap
 		return self::checkBookingAmount( $range[0], $range[1], $booking, $appliedTerms, $allowedTotalBookings );
 	}
 
+	/**
+	 * @param array<int, mixed> $args
+	 *
+	 * @return string
+	 */
 	public static function maxBookingsMonthErrorMessage( array $args ): string {
 		$maxDays  = $args[0];
 		$resetDay = $args[2];
@@ -626,11 +668,11 @@ private static function getBookingMonthRange( Booking $booking, int $resetDay ):
 	 *
 	 * Is often used by BookingRule to determine if a booking should be taken into consideration
 	 *
-	 * @param Booking[] $bookings
-	 * @param \WP_User  $user
-	 * @param             $terms
+	 * @param Booking[]         $bookings
+	 * @param \WP_User          $user
+	 * @param bool|array<mixed> $terms
 	 *
-	 * @return array|null
+	 * @return Booking[]|null
 	 */
 	private static function filterBookingsForTermsAndUser( array $bookings, \WP_User $user, $terms ): ?array {
 		$filteredTerms = Booking::filterTermsApply( $bookings, $terms );
@@ -661,7 +703,7 @@ public static function hasDefaultSettings(): bool {
 	 *
 	 * @return Booking[]
 	 */
-	private static function filterEmptyBookings( array $bookings ) {
+	private static function filterEmptyBookings( array $bookings ): array {
 		return array_filter( $bookings, fn( $booking ) => $booking->getDuration() > 0 );
 	}
 
@@ -672,13 +714,13 @@ private static function filterEmptyBookings( array $bookings ) {
 	 * Will return the conflicting bookings if a user has too many in the range.
 	 * Will also consider the setting if cancelled bookings should be considered.
 	 *
-	 * @param DateTime    $startOfRange
-	 * @param DateTime    $endOfRange
-	 * @param Booking     $booking
-	 * @param array|false $appliedTerms
-	 * @param int         $allowedBookableDays
+	 * @param DateTime          $startOfRange
+	 * @param DateTime          $endOfRange
+	 * @param Booking           $booking
+	 * @param bool|array<mixed> $appliedTerms
+	 * @param int               $allowedBookableDays
 	 *
-	 * @return array|null - conflicting bookings in order of post_date
+	 * @return Booking[]|null - conflicting bookings in order of post_date
 	 * @throws Exception
 	 */
 	private static function checkBookingRangeForDays( DateTime $startOfRange, DateTime $endOfRange, Booking $booking, $appliedTerms, int $allowedBookableDays ): ?array {
@@ -723,16 +765,16 @@ private static function checkBookingRangeForDays( DateTime $startOfRange, DateTi
 	 * Will return the conflicting bookings if a user has too many in the range.
 	 * Cancelled bookings will be considered when they were cancelled after the start of the range.
 	 *
-	 * @param DateTime $startOfRange
-	 * @param DateTime $endOfRange
-	 * @param Booking  $booking
-	 * @param $appliedTerms
-	 * @param int      $allowedTotalBookings
+	 * @param DateTime          $startOfRange
+	 * @param DateTime          $endOfRange
+	 * @param Booking           $booking
+	 * @param bool|array<mixed> $appliedTerms
+	 * @param int               $allowedTotalBookings
 	 *
 	 * @return Booking[]|null
 	 * @throws Exception
 	 */
-	private static function checkBookingAmount( DateTime $startOfRange, DateTime $endOfRange, Booking $booking, $appliedTerms, int $allowedTotalBookings ) {
+	private static function checkBookingAmount( DateTime $startOfRange, DateTime $endOfRange, Booking $booking, $appliedTerms, int $allowedTotalBookings ): ?array {
 		$countedPostTypes = [ 'confirmed' ];
 		if ( Settings::getOption( 'commonsbooking_options_restrictions', 'bookingrules-count-cancelled' ) == 'on' ) {
 			$countedPostTypes[] = 'canceled';
diff --git a/src/Service/BookingRuleApplied.php b/src/Service/BookingRuleApplied.php
index a9db1e2b6..66577a1de 100644
--- a/src/Service/BookingRuleApplied.php
+++ b/src/Service/BookingRuleApplied.php
@@ -20,12 +20,15 @@
 class BookingRuleApplied extends BookingRule {
 
 	private bool $appliesToAll;
+	/** @var array<mixed> */
 	private array $appliedTerms;
+	/** @var array<int, mixed> */
 	private array $appliedParams;
 	/**
 	 * @var int|string
 	 */
 	private $appliedSelectParam;
+	/** @var string[] */
 	private array $excludedRoles;
 
 	/**
@@ -51,8 +54,8 @@ public function __construct( BookingRule $rule ) {
 	/**
 	 * Will set what this Booking Rule applies to, either needs to be all or at least one category
 	 *
-	 * @param   bool  $appliesToAll
-	 * @param   array $appliedTerms
+	 * @param   bool          $appliesToAll
+	 * @param   array<mixed>  $appliedTerms
 	 *
 	 * @throws BookingRuleException
 	 */
@@ -67,8 +70,8 @@ public function setAppliesToWhat( bool $appliesToAll, array $appliedTerms = [] )
 	/**
 	 * Will set the necessary params for the BookingRule to work
 	 *
-	 * @param   array      $paramsToSet needs to be numeric
-	 * @param   int|string $selectParam needs to be numeric
+	 * @param   array<int, mixed>  $paramsToSet needs to be numeric
+	 * @param   int|string|null    $selectParam needs to be numeric
 	 *
 	 * @throws BookingRuleException - if not enough params were specified for the BookingRule
 	 */
@@ -96,7 +99,7 @@ public function setAppliedParams( array $paramsToSet, $selectParam ): void {
 	/**
 	 * Sets the roles that the rule will not apply to
 	 *
-	 * @param   array $excludedRoles
+	 * @param   string[] $excludedRoles
 	 */
 	public function setExcludedRoles( array $excludedRoles ): void {
 		$this->excludedRoles = $excludedRoles;
@@ -109,7 +112,7 @@ public function setExcludedRoles( array $excludedRoles ): void {
 	 *
 	 * @param Booking $booking - The booking object to check for rule compliance
 	 *
-	 * @return array|null - An array of conflicting bookings or an empty array if the booking complies with all rules
+	 * @return Booking[]|null - An array of conflicting bookings or null if the booking complies with all rules
 	 */
 	public function checkBookingCompliance( Booking $booking ): ?array {
 		if ( $booking->isBookingOwnerPrivileged() ) {
diff --git a/src/Service/Holiday.php b/src/Service/Holiday.php
index 82338030e..2596a2901 100644
--- a/src/Service/Holiday.php
+++ b/src/Service/Holiday.php
@@ -8,15 +8,15 @@ class Holiday {
 	 * Will render the fields in the timeframe settings where the user can define the holidays to get for the different German states and years.
 	 * The actual holidays will be loaded through feiertagejs.
 	 *
-	 * @param $field
-	 * @param $value
-	 * @param $object_id
-	 * @param $object_type
-	 * @param $field_type
+	 * @param mixed $field
+	 * @param mixed $value
+	 * @param mixed $object_id
+	 * @param mixed $object_type
+	 * @param mixed $field_type
 	 *
 	 * @return string
 	 */
-	public static function renderFields( $field, $value, $object_id, $object_type, $field_type ) {
+	public static function renderFields( $field, $value, $object_id, $object_type, $field_type ): string {
 
 		// make sure we specify each part of the value we need.
 		$value = wp_parse_args(
diff --git a/src/Service/MassOperations.php b/src/Service/MassOperations.php
index 35b7d6c57..d82312a2d 100644
--- a/src/Service/MassOperations.php
+++ b/src/Service/MassOperations.php
@@ -4,7 +4,7 @@
 
 class MassOperations {
 
-	public static function ajaxMigrateOrphaned() {
+	public static function ajaxMigrateOrphaned(): void {
 		check_ajax_referer( 'cb_orphaned_booking_migration', 'nonce' );
 
 		if ( $_POST['data'] == 'false' ) {
diff --git a/src/Service/Scheduler.php b/src/Service/Scheduler.php
index 8f7fc65f6..d642f275a 100644
--- a/src/Service/Scheduler.php
+++ b/src/Service/Scheduler.php
@@ -28,12 +28,12 @@ class Scheduler {
 	 * It also hooks the appropriate actions that will un-schedule the job upon certain changes.
 	 * We can safely un-schedule the job upon changes, because the job will be re-scheduled with the correct settings when the page is loaded again.
 	 *
-	 * @param string   $jobhook the action hook to run when the event is executed
-	 * @param callable $callback the callback function of that hook
-	 * @param string   $reccurence how often the event should subsequently recur
-	 * @param string   $executionTime takes time of day the job should be executed, only for daily reccurence
-	 * @param array    $option first element is the options_key, second is the field_id. If set, the field is checked and determines wether the hook should be ran
-	 * @param string   $updateHook The WordPress hook that should update the option
+	 * @param string        $jobhook the action hook to run when the event is executed
+	 * @param callable      $callback the callback function of that hook
+	 * @param string        $reccurence how often the event should subsequently recur
+	 * @param string        $executionTime takes time of day the job should be executed, only for daily reccurence
+	 * @param array<string> $option first element is the options_key, second is the field_id. If set, the field is checked and determines wether the hook should be ran
+	 * @param string        $updateHook The WordPress hook that should update the option
 	 */
 	function __construct(
 		string $jobhook,
@@ -91,7 +91,7 @@ function () {
 	/**
 	 * Returns array with custom time intervals.
 	 *
-	 * @return array[]
+	 * @return array<string, array{display: string, interval: int}>
 	 */
 	public static function getIntervals(): array {
 		return array(
@@ -117,11 +117,11 @@ public static function getIntervals(): array {
 	/**
 	 * Inits custom intervals.
 	 *
-	 * @param $schedules
+	 * @param array<string, array<string, mixed>> $schedules
 	 *
-	 * @return array
+	 * @return array<string, array<string, mixed>>
 	 */
-	public static function initIntervals( $schedules ): array {
+	public static function initIntervals( array $schedules ): array {
 		return array_merge( $schedules, self::getIntervals() );
 	}
 
@@ -132,7 +132,7 @@ public static function initIntervals( $schedules ): array {
 	 *
 	 * @return void
 	 */
-	public static function initHooks() {
+	public static function initHooks(): void {
 		// Init booking cleanup job
 		new Scheduler(
 			'cleanup',
@@ -251,7 +251,7 @@ private function unscheduleJob() {
 	 * There are also jobs still from CommonsBooking 0.X listed here.
 	 * It is important to remove the jobs, because WordPress does not delete them on it's own, not even on plugin deactivation.
 	 */
-	public static function unscheduleOldEvents() {
+	public static function unscheduleOldEvents(): void {
 		$cbCronHooks = [
 			'cb_cron_hook',
 			'cb_reminder_cron_hook',
diff --git a/src/Service/TimeframeExport.php b/src/Service/TimeframeExport.php
index b7d89dd24..c0b6ac7ca 100644
--- a/src/Service/TimeframeExport.php
+++ b/src/Service/TimeframeExport.php
@@ -30,19 +30,19 @@ class TimeframeExport {
 	/**
 	 * The extra meta fields to export for locations.
 	 *
-	 * @var array|null
+	 * @var string[]|null
 	 */
 	private ?array $locationFields = null;
 	/**
 	 * The extra meta fields to export for items.
 	 *
-	 * @var array|null
+	 * @var string[]|null
 	 */
 	private ?array $itemFields = null;
 	/**
 	 * The extra meta fields to export for users.
 	 *
-	 * @var array|null
+	 * @var string[]|null
 	 */
 	private ?array $userFields = null;
 	/**
@@ -112,9 +112,9 @@ class TimeframeExport {
 	 * @param string      $exportStartDate Start date string of export
 	 * @param string      $exportEndDate End date string of export
 	 *
-	 * @param array|null  $locationFields Metafields of location objects that should be included in the export
-	 * @param array|null  $itemFields Metafields of item objects that should be included in the export
-	 * @param array|null  $userFields Metafields of user objects that should be included in the export
+	 * @param string[]|null  $locationFields Metafields of location objects that should be included in the export
+	 * @param string[]|null  $itemFields Metafields of item objects that should be included in the export
+	 * @param string[]|null  $userFields Metafields of user objects that should be included in the export
 	 * @param int|null    $lastProcessedPage 0 when starting, otherwise the last processed page from previous run
 	 * @param int|null    $totalPosts Set on previous run, total amount of posts in export
 	 * @param string|null $transientName Set on previous run, name of transient where intermediate results are stored
@@ -435,11 +435,11 @@ private function getProgressString(): string {
 	/**
 	 * Return user defined export fields.
 	 *
-	 * @param $inputName
+	 * @param string $inputName
 	 *
-	 * @return false|string[]
+	 * @return string[]
 	 */
-	protected static function getInputFields( $inputName ) {
+	protected static function getInputFields( string $inputName ): array {
 		$inputFieldsString =
 			array_key_exists( $inputName, $_REQUEST ) ? sanitize_text_field( $_REQUEST[ $inputName ] ) :
 				Settings::getOption( 'commonsbooking_options_export', '$inputName' );
@@ -535,7 +535,7 @@ public function getExportData( int $page = - 1 ): bool {
 	 *
 	 * @return DatePeriod
 	 */
-	protected static function getPeriod( $start, $end ) {
+	protected static function getPeriod( string $start, string $end ): \DatePeriod {
 		// Timerange
 		$begin = Wordpress::getUTCDateTime( $start );
 		$end   = Wordpress::getUTCDateTime( $end );
@@ -572,7 +572,7 @@ protected static function getType(): int {
 	 *
 	 * @param int[] $timeframeIDs Array of timeframe post IDs
 	 *
-	 * @return array
+	 * @return array<int, array<string, mixed>>
 	 */
 	public static function getTimeframeData( array $timeframeIDs ): array {
 
@@ -670,7 +670,7 @@ function ( $location ) {
 	 *
 	 * @param \CommonsBooking\Model\Timeframe $timeframe The timeframe object to process
 	 *
-	 * @return array
+	 * @return array<string, mixed>
 	 */
 	protected static function getRelevantTimeframeFields( \CommonsBooking\Model\Timeframe $timeframe ): array {
 		$postArray               = get_object_vars( $timeframe->getPost() );
diff --git a/src/Service/Upgrade.php b/src/Service/Upgrade.php
index c74854a24..f34cf6632 100644
--- a/src/Service/Upgrade.php
+++ b/src/Service/Upgrade.php
@@ -36,7 +36,7 @@ class Upgrade {
 	 *
 	 * This is so that once the upgrade from a specific version has been run, it will not be run again.
 	 *
-	 * @var array[]
+	 * @var array<string, array<int, array<int, string>>>
 	 */
 	private static array $upgradeTasks = [
 		'2.6.0' => [
@@ -71,7 +71,7 @@ class Upgrade {
 	 *
 	 * ATTENTION: These tasks will be ignored upon new installations.
 	 *
-	 * @var array|array[]
+	 * @var array<string, array<int, array<int, string>>>
 	 */
 	private static array $ajaxUpgradeTasks = [
 		'2.8.5' => [
@@ -173,11 +173,11 @@ public function runUpgradeTasks(): void {
 	/**
 	 * Returns an array of tasks that need to be run for this upgrade.
 	 *
-	 * @param $upgradeTasks - An associative array with the version as key and the tasks as value (array of tasks).
+	 * @param array<string, array<int, array<int, string>>> $upgradeTasks An associative array with the version as key and the tasks as value.
 	 *
-	 * @return array
+	 * @return array<int, array<int, string>>
 	 */
-	private function getTasksForUpgrade( $upgradeTasks ): array {
+	private function getTasksForUpgrade( array $upgradeTasks ): array {
 		$tasks = [];
 		foreach ( $upgradeTasks as $version => $versionTasks ) {
 			if ( version_compare( $this->previousVersion, $version, '<' ) && version_compare( $this->currentVersion, $version, '>=' ) ) {
diff --git a/src/Service/iCalendar.php b/src/Service/iCalendar.php
index 8e902f853..95af01929 100755
--- a/src/Service/iCalendar.php
+++ b/src/Service/iCalendar.php
@@ -109,12 +109,12 @@ public static function getCurrentUserCalendarLink() {
 	/**
 	 * Get the ics file for an existing booking. Will be called, when the "Add to Calendar" button on the booking page is pressed
 	 *
-	 * @param $bookingID
+	 * @param int $bookingID
 	 *
 	 * @return void
 	 * @throws \Exception
 	 */
-	public static function downloadICS( $bookingID ): void {
+	public static function downloadICS( int $bookingID ): void {
 		$postID           = $bookingID;
 		$booking          = new Booking( $postID );
 		$template_objects = [
@@ -150,7 +150,7 @@ public function addBookingEvent(
 		Booking $booking,
 		string $eventTitle,
 		string $eventDescription
-	) {
+	): void {
 			$eventDescription = preg_replace( "/(^[\r\n]*|[\r\n]+)[\s\t]*[\r\n]+/", "\n", $eventDescription ); // remove empty lines from the description, they are not part of the standard
 
 			$bookingLocation           = $booking->getLocation();
diff --git a/src/Settings/Settings.php b/src/Settings/Settings.php
index 0bd718aaf..bdb601115 100644
--- a/src/Settings/Settings.php
+++ b/src/Settings/Settings.php
@@ -72,7 +72,7 @@ public static function updateOption( $option_name, $field_id, $field_value ) {
 	}
 
 
-	public static function returnFormattedMetaboxFields( $postType ) {
+	public static function returnFormattedMetaboxFields( string $postType ): string {
 		$metabox_array = self::getOption( 'commonsbooking_settings_metaboxfields', $postType );
 
 		$result = '<br>';
diff --git a/src/View/Admin/Filter.php b/src/View/Admin/Filter.php
index 7b03abe61..5bd4d2015 100644
--- a/src/View/Admin/Filter.php
+++ b/src/View/Admin/Filter.php
@@ -7,12 +7,14 @@ class Filter {
 	/**
 	 * Renders backend list filter.
 	 *
-	 * @param $postType
-	 * @param $label
-	 * @param $key
-	 * @param $values
+	 * @param string               $postType
+	 * @param string               $label
+	 * @param string               $key
+	 * @param array<string, mixed> $values
+	 *
+	 * @return void
 	 */
-	public static function renderFilter( $postType, $label, $key, $values ) {
+	public static function renderFilter( string $postType, string $label, string $key, array $values ): void {
 		// only add filter to post type you want
 		if ( isset( $_GET['post_type'] ) && $postType == $_GET['post_type'] ) {
 			?>
@@ -37,13 +39,15 @@ public static function renderFilter( $postType, $label, $key, $values ) {
 	/**
 	 * Renders Start-/Enddate filters for admin lists.
 	 *
-	 * @param $postType
-	 * @param $startDateInputName
-	 * @param $endDateInputName
-	 * @param $from
-	 * @param $to
+	 * @param string $postType
+	 * @param string $startDateInputName
+	 * @param string $endDateInputName
+	 * @param string $from
+	 * @param string $to
+	 *
+	 * @return void
 	 */
-	public static function renderDateFilter( $postType, $startDateInputName, $endDateInputName, $from, $to ) {
+	public static function renderDateFilter( string $postType, string $startDateInputName, string $endDateInputName, string $from, string $to ): void {
 		if ( isset( $_GET['post_type'] ) && $postType == sanitize_text_field( $_GET['post_type'] ) ) {
 			echo '<style>
                 input[name=' . commonsbooking_sanitizeHTML( $startDateInputName ) . '], 
diff --git a/src/View/Booking.php b/src/View/Booking.php
index 0c3ded1dc..97fb08471 100755
--- a/src/View/Booking.php
+++ b/src/View/Booking.php
@@ -442,12 +442,12 @@ public static function getBookingCode_AJAX() {
 	 *
 	 * A list of items with timeframes.
 	 *
-	 * @param $atts
+	 * @param array<string, mixed> $atts
 	 *
 	 * @return false|string
 	 * @throws Exception
 	 */
-	public static function shortcode( $atts ) {
+	public static function shortcode( array $atts ) {
 		global $templateData;
 		$templateData = [];
 		$templateData = self::getBookingListData();
@@ -497,7 +497,7 @@ public static function getError(): string {
 	 *
 	 * This only includes confirmed bookings in the future.
 	 *
-	 * @param $user
+	 * @param int|\WP_User|null $user
 	 *
 	 * @return string|false
 	 * @throws Exception
@@ -556,10 +556,12 @@ public static function getBookingListiCal( $user = null ) {
 	/**
 	 * Callback function to render the button that submits the backend booking.
 	 *
-	 * @param $field_args
-	 * @param $field
+	 * @param array<string, mixed> $field_args
+	 * @param \CMB2_Field          $field
+	 *
+	 * @return void
 	 */
-	public static function renderSubmitButton( $field_args, $field ) {
+	public static function renderSubmitButton( array $field_args, \CMB2_Field $field ): void {
 		$id     = $field->args( 'id' );
 		$label  = $field->args( 'name' );
 		$desc   = $field->args( 'desc' );
diff --git a/src/View/BookingCodes.php b/src/View/BookingCodes.php
index 02a1b917d..df22d16fc 100644
--- a/src/View/BookingCodes.php
+++ b/src/View/BookingCodes.php
@@ -97,13 +97,13 @@ public static function cronEmailCodesSaved( $updated, $action, $field ): void {
 	 * CMB2 sanitize field callback
 	 * Will take the entered start date and saves it as a timestamp.
 	 *
-	 * @param  mixed       $value      The unsanitized value from the form.
-	 * @param  array       $field_args Array of field arguments.
-	 * @param  \CMB2_Field $field      The field object
+	 * @param  mixed                $value      The unsanitized value from the form.
+	 * @param  array<string, mixed> $field_args Array of field arguments.
+	 * @param  \CMB2_Field          $field      The field object
 	 *
-	 * @return ?array                  Sanitized value to be stored.
+	 * @return array<string, mixed>|null         Sanitized value to be stored.
 	 */
-	public static function sanitizeCronEmailCodes( $value, $field_args, $field ): ?array {
+	public static function sanitizeCronEmailCodes( $value, array $field_args, $field ): ?array {
 		if ( $value == null ) {
 			return null;
 		}
@@ -128,13 +128,13 @@ public static function sanitizeCronEmailCodes( $value, $field_args, $field ): ?a
 	/**
 	 * CMB2 escape field callback
 	 *
-	 * @param  mixed       $value      The unescaped value from the database.
-	 * @param  array       $field_args Array of field arguments.
-	 * @param  \CMB2_Field $field      The field object
+	 * @param  mixed                $value      The unescaped value from the database.
+	 * @param  array<string, mixed> $field_args Array of field arguments.
+	 * @param  \CMB2_Field          $field      The field object
 	 *
-	 * @return array                  Escaped value to be displayed.
+	 * @return array<string, mixed>             Escaped value to be displayed.
 	 */
-	public static function escapeCronEmailCodes( $value, $field_args, $field ): array {
+	public static function escapeCronEmailCodes( $value, array $field_args, $field ): array {
 
 		if ( is_array( $value ) ) {
 			return array(
@@ -157,13 +157,13 @@ public static function escapeCronEmailCodes( $value, $field_args, $field ): arra
 	/**
 	 * renders custom CMB2 field settings for Cron Booking Codes
 	 *
-	 * @param  $field: The current CMB2_Field object.
-	 * @param  $escaped_value: The value of this field passed through the escaping filter.
-	 * @param  $object_id: The id of the object you are working with. Most commonly, the post id.
-	 * @param  $object_type: The type of object you are working with.
-	 * @param  $field_type_object: This is an instance of the CMB2_Types object and gives you access to all of the methods
+	 * @param  \CMB2_Field $field         The current CMB2_Field object.
+	 * @param  mixed       $escaped_value The value of this field passed through the escaping filter.
+	 * @param  int|string  $object_id     The id of the object you are working with. Most commonly, the post id.
+	 * @param  string      $object_type   The type of object you are working with.
+	 * @param  \CMB2_Types $field_type    This is an instance of the CMB2_Types object and gives you access to all of the methods
 	 */
-	public static function renderCronEmailFields( $field, $escaped_value, $object_id, $object_type, $field_type ): void {
+	public static function renderCronEmailFields( \CMB2_Field $field, $escaped_value, $object_id, string $object_type, \CMB2_Types $field_type ): void {
 
 		$timeframeId = $object_id;
 		$timeframe   = new Timeframe( $timeframeId );
@@ -263,10 +263,12 @@ public static function renderCronEmailFields( $field, $escaped_value, $object_id
 	/**
 	 * renders CMB2 field row
 	 *
-	 * @param  array       $field_args Array of field arguments.
-	 * @param  \CMB2_Field $field      The field object
+	 * @param  array<string, mixed> $field_args Array of field arguments.
+	 * @param  \CMB2_Field          $field      The field object
+	 *
+	 * @return bool
 	 */
-	public static function renderDirectEmailRow( $field_args, $field ) {
+	public static function renderDirectEmailRow( array $field_args, \CMB2_Field $field ): bool {
 
 		$timeframeId = $field->object_id();
 		$timeframe   = new Timeframe( $timeframeId );
@@ -372,13 +374,15 @@ public static function renderDirectEmailRow( $field_args, $field ) {
 	/**
 	 * Renders table of booking codes.
 	 *
-	 * @param $timeframeId
+	 * @param int $timeframeId
+	 *
+	 * @return bool
 	 */
-	public static function renderTable( $timeframeId ) {
+	public static function renderTable( int $timeframeId ): bool {
 		try {
 			$timeframe = new Timeframe( $timeframeId );} catch ( BookingCodeException $e ) {
 			echo $e->getMessage();
-			return;
+			return false;
 			}
 
 			echo '
@@ -464,8 +468,10 @@ public static function renderBookingCodesTable( $bookingCodes ): string {
 	 * Renders CVS file (txt-format) with booking codes for download
 	 *
 	 * @param int|null $timeframeId
+	 *
+	 * @return void
 	 */
-	public static function renderCSV( $timeframeId = null ) {
+	public static function renderCSV( ?int $timeframeId = null ): void {
 		if ( $timeframeId == null ) {
 			$timeframeId = intval( $_GET['post'] );
 		}
@@ -495,11 +501,13 @@ public static function renderCSV( $timeframeId = null ) {
 	/**
 	 * action for sending Booking Codes by E-mail
 	 *
-	 * @param int $timeframeId      ID of requested timeframe
-	 * @param int $tsFrom           Timestamp of first Booking Code
-	 * @param int $tsTo             Timestamp of last Booking Code
+	 * @param int|null $timeframeId      ID of requested timeframe
+	 * @param int|null $tsFrom           Timestamp of first Booking Code
+	 * @param int|null $tsTo             Timestamp of last Booking Code
+	 *
+	 * @return void
 	 */
-	public static function emailCodes( $timeframeId = null, $tsFrom = null, $tsTo = null ) {
+	public static function emailCodes( ?int $timeframeId = null, ?int $tsFrom = null, ?int $tsTo = null ): void {
 
 		if ( $timeframeId == null ) {
 			$timeframeId = empty( $_GET['post'] ) ? null : sanitize_text_field( $_GET['post'] );
diff --git a/src/View/Calendar.php b/src/View/Calendar.php
index dba371928..4c94cc88e 100644
--- a/src/View/Calendar.php
+++ b/src/View/Calendar.php
@@ -34,7 +34,7 @@ class Calendar {
 	 * Many thanks to fLotte Berlin!
 	 * Forked from https://github.com/flotte-berlin/cb-shortcodes/blob/master/custom-shortcodes-cb-items.php
 	 *
-	 * @param $atts array Supports the following attributes:
+	 * @param array<string, mixed> $atts Supports the following attributes:
 	 *                    - locationcat: Filter by location category
 	 *                    - itemcat: Filter by item category
 	 *                    - days: Number of days to show in calendar table view
@@ -43,19 +43,19 @@ class Calendar {
 	 * @return string
 	 * @throws Exception
 	 */
-	public static function renderTable( $atts ): string {
+	public static function renderTable( array $atts ): string {
 		$locationCategory = false;
-		if ( is_array( $atts ) && array_key_exists( 'locationcat', $atts ) ) {
+		if ( array_key_exists( 'locationcat', $atts ) ) {
 			$locationCategory = $atts['locationcat'];
 		}
 		$itemCategory = false;
-		if ( is_array( $atts ) && array_key_exists( 'itemcat', $atts ) ) {
+		if ( array_key_exists( 'itemcat', $atts ) ) {
 			$itemCategory = $atts['itemcat'];
 		}
 
 		// defines the number of days shown in the calendar table view. If not set, default is 31 days
 		// TODO: max days should be made configurable in options
-		$days = is_array( $atts ) && array_key_exists( 'days', $atts ) ? $atts['days'] : 31;
+		$days = array_key_exists( 'days', $atts ) ? $atts['days'] : 31;
 
 		$desc  = $atts['desc'] ?? '';
 		$date  = Wordpress::getUTCDateTimeByTimestamp( current_time( 'timestamp' ) );
@@ -185,7 +185,12 @@ public static function renderTable( $atts ): string {
 		return $print;
 	}
 
-	public static function shortcode( $atts ) {
+	/**
+	 * @param array<string, mixed> $atts
+	 * @return string|null
+	 * @throws \Exception
+	 */
+	public static function shortcode( array $atts ): ?string {
 		global $templateData;
 		$templateData         = [];
 		$templateData['data'] = self::renderTable( $atts );
@@ -195,16 +200,18 @@ public static function shortcode( $atts ) {
 			commonsbooking_get_template_part( 'shortcode', 'items_table', true, false, false );
 			return ob_get_clean();
 		}
+
+		return null;
 	}
 
 	/**
 	 * Renders months in headline.
 	 *
-	 * @param $month_cols
+	 * @param array<string, int> $month_cols
 	 *
 	 * @return string
 	 */
-	protected static function renderHeadlineMonths( $month_cols ): string {
+	protected static function renderHeadlineMonths( array $month_cols ): string {
 		$print = '';
 		foreach ( $month_cols as $month => $colspan ) {
 			$print .= "<th class='sortless' colspan='" . $colspan . "'>";
@@ -222,11 +229,11 @@ protected static function renderHeadlineMonths( $month_cols ): string {
 	/**
 	 * Renders days in headline.
 	 *
-	 * @param $days_display
+	 * @param array<int, string> $days_display
 	 *
 	 * @return string
 	 */
-	protected static function renderHeadlineDays( $days_display ): string {
+	protected static function renderHeadlineDays( array $days_display ): string {
 		$divider = "</th><th class='cal sortless'>";
 		$dayStr  = implode( $divider, $days_display );
 
@@ -237,18 +244,18 @@ protected static function renderHeadlineDays( $days_display ): string {
 	/**
 	 * Renders item/location row.
 	 *
-	 * @param $item
-	 * @param $locationId
-	 * @param $locationName
-	 * @param $today
-	 * @param $last_day
-	 * @param $days
-	 * @param $days_display
+	 * @param \WP_Post           $item
+	 * @param int                $locationId
+	 * @param string             $locationName
+	 * @param string             $today
+	 * @param string             $last_day
+	 * @param int                $days
+	 * @param array<int, string> $days_display
 	 *
 	 * @return string
 	 * @throws Exception
 	 */
-	protected static function renderItemLocationRow( $item, $locationId, $locationName, $today, $last_day, $days, $days_display ): string {
+	protected static function renderItemLocationRow( \WP_Post $item, int $locationId, string $locationName, string $today, string $last_day, int $days, array $days_display ): string {
 		$cacheItem = Plugin::getCacheItem();
 		if ( $cacheItem ) {
 			return $cacheItem;
@@ -338,7 +345,7 @@ protected static function renderItemLocationRow( $item, $locationId, $locationNa
 	 * @param string                        $endDateString YYYY-MM-DD Format
 	 * @param bool                          $keepDaterange
 	 *
-	 * @return array
+	 * @return array<string, mixed>
 	 * @throws Exception
 	 */
 	public static function getCalendarDataArray( $item, $location, string $startDateString, string $endDateString, bool $keepDaterange = false ): array {
@@ -413,11 +420,11 @@ public static function getCalendarDataArray( $item, $location, string $startDate
 	/**
 	 * Returns closest timeframe from date/time perspective.
 	 *
-	 * @param $bookableTimeframes
+	 * @param array<int, \CommonsBooking\Model\Timeframe> $bookableTimeframes
 	 *
 	 * @return \CommonsBooking\Model\Timeframe|null
 	 */
-	public static function getClosestBookableTimeFrameForToday( $bookableTimeframes ): ?\CommonsBooking\Model\Timeframe {
+	public static function getClosestBookableTimeFrameForToday( array $bookableTimeframes ): ?\CommonsBooking\Model\Timeframe {
 		$today           = new Day( date( 'Y-m-d' ) );
 		$todayTimeframes = \CommonsBooking\Repository\Timeframe::filterTimeframesForTimerange( $bookableTimeframes, $today->getStartTimestamp(), $today->getEndTimestamp() );
 		$todayTimeframes = array_filter(
@@ -523,12 +530,15 @@ private static function getMobileCalendarMonthCount(): int {
 	 *
 	 * Uses cache which expires at midnight on a daily basis.
 	 *
-	 * @param Day   $startDate
-	 * @param Day   $endDate
-	 * @param array $locations []
-	 * @param array $items <int|string>
+	 * @param Day        $startDate
+	 * @param Day        $endDate
+	 * @param array<int, int|string> $locations
+	 * @param array<int, int|string> $items
+	 * @param int|null   $advanceBookingDays
+	 * @param int|null   $lastBookableDate
+	 * @param string|null $firstBookableDay
 	 *
-	 * @return array
+	 * @return array<string, mixed>
 	 * @throws Exception
 	 */
 	public static function prepareJsonResponse(
@@ -536,9 +546,9 @@ public static function prepareJsonResponse(
 		Day $endDate,
 		array $locations,
 		array $items,
-		$advanceBookingDays = null,
-		$lastBookableDate = null,
-		$firstBookableDay = null
+		?int $advanceBookingDays = null,
+		?int $lastBookableDate = null,
+		?string $firstBookableDay = null
 	): array {
 
 		$current_user   = wp_get_current_user();
@@ -634,14 +644,15 @@ public static function prepareJsonResponse(
 	/**
 	 * Processes day for calendar view of json.
 	 *
-	 * @param Day $day
-	 * @param $lastBookableDate
-	 * @param $endDate
-	 * @param $jsonResponse
+	 * @param Day                    $day
+	 * @param int                    $lastBookableDate
+	 * @param Day                    $endDate
+	 * @param array<string, mixed>   $jsonResponse
+	 * @param string|null            $firstBookableDay
 	 *
 	 * @return void
 	 */
-	protected static function mapDay( $day, $lastBookableDate, $endDate, &$jsonResponse, $firstBookableDay ) {
+	protected static function mapDay( Day $day, int $lastBookableDate, Day $endDate, array &$jsonResponse, ?string $firstBookableDay ): void {
 		$dayArray = [
 			'date'               => $day->getFormattedDate( 'd.m.Y' ),
 			'slots'              => [],
@@ -722,13 +733,15 @@ protected static function mapDay( $day, $lastBookableDate, $endDate, &$jsonRespo
 	/**
 	 * Extracts calendar relevant data from slot.
 	 *
-	 * @param $slot
-	 * @param $dayArray
-	 * @param $jsonResponse
-	 * @param $allLocked
-	 * @param $noSlots
+	 * @param array<string, mixed>  $slot
+	 * @param array<string, mixed>  $dayArray
+	 * @param array<string, mixed>  $jsonResponse
+	 * @param bool                  $allLocked
+	 * @param bool                  $noSlots
+	 *
+	 * @return void
 	 */
-	protected static function processSlot( $slot, &$dayArray, &$jsonResponse, &$allLocked, &$noSlots ) {
+	protected static function processSlot( array $slot, array &$dayArray, array &$jsonResponse, bool &$allLocked, bool &$noSlots ): void {
 		// Add only bookable slots for time select
 		// TODO: This should be refactored to use the methods on the timeframe model.
 		if ( ! empty( $slot['timeframe'] ) && $slot['timeframe'] instanceof WP_Post ) {
@@ -816,7 +829,7 @@ protected static function processSlot( $slot, &$dayArray, &$jsonResponse, &$allL
 	/**
 	 * @param Day $day
 	 *
-	 * @return array
+	 * @return array<string, mixed>
 	 */
 	protected static function getLockedDayArray( Day $day ): array {
 		return [
@@ -837,8 +850,9 @@ protected static function getLockedDayArray( Day $day ): array {
 	 * Ajax request - Returns json-formatted calendardata.
 	 *
 	 * @throws Exception
+	 * @return void
 	 */
-	public static function getCalendarData() {
+	public static function getCalendarData(): void {
 		// item by post-param
 		$item = isset( $_POST['item'] ) && $_POST['item'] != '' ? intval( $_POST['item'] ) : false;
 		if ( $item === false || $item == 0 ) { // 0 = failed intval check
diff --git a/src/View/Dashboard.php b/src/View/Dashboard.php
index 87e00abe7..abb171e4a 100644
--- a/src/View/Dashboard.php
+++ b/src/View/Dashboard.php
@@ -7,7 +7,7 @@
  */
 class Dashboard extends View {
 
-	public static function index() {
+	public static function index(): void {
 		ob_start();
 		commonsbooking_sanitizeHTML( commonsbooking_get_template_part( 'dashboard', 'index' ) );
 		echo ob_get_clean();
@@ -27,7 +27,7 @@ public static function renderBeginningBookings() {
 			$beginningBookings = array_filter(
 				$beginningBookings,
 				function ( $beginningBooking ) {
-					return commonsbooking_isCurrentUserAllowedToEdit( $beginningBooking );
+					return commonsbooking_isCurrentUserAllowedToEdit( $beginningBooking->ID );
 				}
 			);
 		}
@@ -72,7 +72,7 @@ public static function renderEndingBookings() {
 			$endingBookings = array_filter(
 				$endingBookings,
 				function ( $endingBooking ) {
-					return commonsbooking_isCurrentUserAllowedToEdit( $endingBooking );
+					return commonsbooking_isCurrentUserAllowedToEdit( $endingBooking->ID );
 				}
 			);
 		}
diff --git a/src/View/Item.php b/src/View/Item.php
index 2bf126eb9..1e8ca857e 100644
--- a/src/View/Item.php
+++ b/src/View/Item.php
@@ -14,7 +14,7 @@ class Item extends View {
 	 *
 	 * @param WP_Post|null $post
 	 *
-	 * @return array
+	 * @return array<string, mixed>
 	 * @throws Exception
 	 */
 	public static function getTemplateData( ?WP_Post $post = null ) {
@@ -89,7 +89,7 @@ function ( \CommonsBooking\Model\Location $location ) {
 	 *
 	 * A list of items with timeframes.
 	 *
-	 * @param $atts
+	 * @param array<string, mixed>|string $atts
 	 *
 	 * @return false|string
 	 * @throws Exception
diff --git a/src/View/Location.php b/src/View/Location.php
index 89bf0257a..37c9cd985 100644
--- a/src/View/Location.php
+++ b/src/View/Location.php
@@ -14,7 +14,7 @@ class Location extends View {
 	 *
 	 * @param WP_Post|null $post
 	 *
-	 * @return array
+	 * @return array<string, mixed>
 	 * @throws Exception
 	 */
 	public static function getTemplateData( ?WP_Post $post = null ): array {
@@ -85,7 +85,7 @@ function ( \CommonsBooking\Model\Item $item ) {
 	 *
 	 * A list of locations with timeframes.
 	 *
-	 * @param $atts
+	 * @param array<string, mixed>|string $atts
 	 *
 	 * @return false|string
 	 * @throws Exception
diff --git a/src/View/Map.php b/src/View/Map.php
index e109b2152..6d5605a4c 100644
--- a/src/View/Map.php
+++ b/src/View/Map.php
@@ -11,8 +11,16 @@ class Map extends View {
 
 	/**
 	 * load needed assets for the map that provides fine tuning of the location's position
+	 *
+	 * @param \CMB2_Field $field
+	 * @param mixed       $escaped_value
+	 * @param int|string  $object_id
+	 * @param string      $object_type
+	 * @param \CMB2_Types $field_type_object
+	 *
+	 * @return void
 	 **/
-	public static function render_cb_map( $field, $escaped_value, $object_id, $object_type, $field_type_object ) {
+	public static function render_cb_map( \CMB2_Field $field, $escaped_value, $object_id, string $object_type, \CMB2_Types $field_type_object ): void {
 		// map
 		wp_enqueue_style( 'cb-leaflet' );
 		wp_enqueue_script( 'cb-leaflet' );
@@ -28,7 +36,7 @@ public static function render_cb_map( $field, $escaped_value, $object_id, $objec
 		wp_add_inline_script( 'cb-map-positioning_js', 'cb_map_positioning.defaults =' . wp_json_encode( $defaults ) );
 	}
 
-	public static function renderGeoRefreshButton() {
+	public static function renderGeoRefreshButton(): void {
 		echo '<div class="cmb-row cmb-type-text ">
 			<div class="cmb-th">
 				<label>' . esc_html__( 'Set / Update GPS Coordinates', 'commonsbooking' ) . '</label>
diff --git a/src/View/MassOperations.php b/src/View/MassOperations.php
index daee0e919..b571ecb09 100644
--- a/src/View/MassOperations.php
+++ b/src/View/MassOperations.php
@@ -3,7 +3,7 @@
 namespace CommonsBooking\View;
 
 class MassOperations {
-	public static function index() {
+	public static function index(): void {
 		global $templateData;
 		$templateData                     = [];
 		$templateData['orphanedBookings'] = \CommonsBooking\Repository\Booking::getOrphaned();
diff --git a/src/View/Migration.php b/src/View/Migration.php
index 201ec729e..fd355600f 100644
--- a/src/View/Migration.php
+++ b/src/View/Migration.php
@@ -14,10 +14,10 @@ class Migration {
 	/**
 	 * Render Migration Form.
 	 *
-	 * @param array      $field_args Array of field arguments.
+	 * @param array<string, mixed> $field_args Array of field arguments.
 	 * @param CMB2_Field $field The field object
 	 */
-	public static function renderMigrationForm( array $field_args, CMB2_Field $field ) {
+	public static function renderMigrationForm( array $field_args, CMB2_Field $field ): void {
 		$cb1Installed = CB1::isInstalled();
 
 		?>
@@ -86,10 +86,10 @@ public static function renderMigrationForm( array $field_args, CMB2_Field $field
 	/**
 	 * Renders booking migration (timeframe to booking cpt) form.
 	 *
-	 * @param array      $field_args
+	 * @param array<string, mixed> $field_args
 	 * @param CMB2_Field $field
 	 */
-	public static function renderBookingMigrationForm( array $field_args, CMB2_Field $field ) {
+	public static function renderBookingMigrationForm( array $field_args, CMB2_Field $field ): void {
 
 		echo( '
             <div class="cmb-row cmb-type-text">
@@ -116,9 +116,13 @@ public static function renderBookingMigrationForm( array $field_args, CMB2_Field
 		);
 	}
 
-	public static function renderUpgradeForm( array $field_args, CMB2_Field $field ) {
+	/**
+	 * @param array<string, mixed> $field_args
+	 * @param CMB2_Field $field
+	 */
+	public static function renderUpgradeForm( array $field_args, CMB2_Field $field ): void {
 		if ( ! Upgrade::isAJAXUpgrade() ) {
-			return false;
+			return;
 		}
 		?>
 		<div class="cmb-row cmb-type-text" id="upgrade-fields">
diff --git a/src/View/Restriction.php b/src/View/Restriction.php
index 27ee1b4ca..608eaa519 100644
--- a/src/View/Restriction.php
+++ b/src/View/Restriction.php
@@ -8,10 +8,10 @@ class Restriction extends View {
 	/**
 	 * Callback function send button.
 	 *
-	 * @param $field_args
-	 * @param $field
+	 * @param array<string, mixed> $field_args
+	 * @param \CMB2_Field $field
 	 */
-	public static function renderSendButton( $field_args, $field ) {
+	public static function renderSendButton( array $field_args, \CMB2_Field $field ): void {
 		$id     = $field->args( 'id' );
 		$label  = $field->args( 'name' );
 		$desc   = $field->args( 'desc' );
diff --git a/src/View/TimeframeExport.php b/src/View/TimeframeExport.php
index 2f1f56003..60931666c 100644
--- a/src/View/TimeframeExport.php
+++ b/src/View/TimeframeExport.php
@@ -16,10 +16,10 @@ class TimeframeExport {
 	const USER_FIELD     = 'user-fields';
 
 	/**
-	 * @param $field_args
-	 * @param $field
+	 * @param array<string, mixed> $field_args
+	 * @param \CMB2_Field $field
 	 */
-	public static function renderExportButton( $field_args, $field ) {
+	public static function renderExportButton( array $field_args, \CMB2_Field $field ): void {
 		?>
 		<div class="cmb-row cmb-type-text ">
 			<div class="cmb-th">
diff --git a/src/View/View.php b/src/View/View.php
index 5c172559f..2dafdc2ff 100644
--- a/src/View/View.php
+++ b/src/View/View.php
@@ -53,7 +53,7 @@ abstract class View {
 	 *
 	 * @param \CommonsBooking\Model\Item|\CommonsBooking\Model\Location $cpt location or item model object to retrieve timeframe data from.
 	 * @param string                                                    $type 'Item' or 'Location'.
-	 * @return array
+	 * @return array<string, mixed>
 	 * @throws Exception
 	 */
 	public static function getShortcodeData( $cpt, string $type ): array {
diff --git a/src/Wordpress/CustomPostType/Booking.php b/src/Wordpress/CustomPostType/Booking.php
index 2d92d7e77..902857867 100644
--- a/src/Wordpress/CustomPostType/Booking.php
+++ b/src/Wordpress/CustomPostType/Booking.php
@@ -73,12 +73,12 @@ public function initHooks() {
 	 * Adds and modifies some booking CPT fields in order to make admin boookings
 	 * compatible to user made bookings via frontend.
 	 *
-	 * @param  mixed $post_id
-	 * @param  mixed $post
-	 * @param  mixed $update
+	 * @param  int $post_id
+	 * @param  \WP_Post|null $post
+	 * @param  bool|null $update
 	 * @return void
 	 */
-	public function savePost( $post_id, $post = null, $update = null ) {
+	public function savePost( int $post_id, ?\WP_Post $post = null, ?bool $update = null ): void {
 		global $pagenow;
 
 		$post            = $post ?? get_post( $post_id );
@@ -171,7 +171,7 @@ public function savePost( $post_id, $post = null, $update = null ) {
 	 *
 	 * @throws BookingDeniedException - if booking is not allowed, contains translated error message for the user
 	 */
-	public static function handleFormRequest() {
+	public static function handleFormRequest(): void {
 		if (
 			function_exists( 'wp_verify_nonce' ) &&
 			isset( $_REQUEST[ static::getWPNonceId() ] ) &&
@@ -287,7 +287,7 @@ public static function handleBookingRequest(
 		);
 
 		// Reject if the slot is already booked by another user (getExistingBookings excludes this booking by ID)
-		if ( $booking && ! commonsbooking_isCurrentUserAllowedToEdit( $booking ) ) {
+		if ( $booking && ! commonsbooking_isCurrentUserAllowedToEdit( $booking->ID ) ) {
 			throw new BookingDeniedException( __( 'There is already a booking in this time-range. This notice may also appear if there is an unconfirmed booking in the requested period. Unconfirmed bookings are deleted after about 10 minutes. Please try again in a few minutes.', 'commonsbooking' ) );
 		}
 
@@ -402,12 +402,13 @@ public static function handleBookingRequest(
 	 * We need to save the grid size for timeframes with full slot grid.
 	 *
 	 * @param $postId
-	 * @param $locationId
-	 * @param $itemId
-	 * @param $startDate
-	 * @param $endDate
+	 * @param int $postId
+	 * @param int $locationId
+	 * @param int $itemId
+	 * @param int $startDate
+	 * @param int $endDate
 	 */
-	private static function saveGridSizes( $postId, $locationId, $itemId, $startDate, $endDate ): void {
+	private static function saveGridSizes( int $postId, int $locationId, int $itemId, int $startDate, int $endDate ): void {
 		$startTimeFrame = \CommonsBooking\Repository\Timeframe::getByLocationItemTimestamp( $locationId, $itemId, $startDate );
 		if ( $startTimeFrame && ! $startTimeFrame->isFullDay() && $startTimeFrame->getGrid() == 0 ) {
 			update_post_meta(
@@ -433,7 +434,7 @@ public static function getView() {
 		return new \CommonsBooking\View\Booking();
 	}
 
-	public function initListView() {
+	public function initListView(): void {
 		if ( array_key_exists( 'post_type', $_GET ) && static::$postType !== $_GET['post_type'] ) {
 			return;
 		}
@@ -484,11 +485,11 @@ public function getTemplate( $content ) {
 	/**
 	 * Is triggered when post gets updated. Currently used to send notifications regarding bookings.
 	 *
-	 * @param $post_ID
-	 * @param $post_after
-	 * @param $post_before
+	 * @param int $post_ID
+	 * @param \WP_Post $post_after
+	 * @param \WP_Post $post_before
 	 */
-	public function postUpdated( $post_ID, $post_after, $post_before ) {
+	public function postUpdated( int $post_ID, \WP_Post $post_after, \WP_Post $post_before ): void {
 
 		if ( ! $this->hasRunBefore( __FUNCTION__ ) ) {
 			$isBooking = get_post_meta( $post_ID, 'type', true ) == Timeframe::BOOKING_ID;
@@ -516,9 +517,9 @@ public function postUpdated( $post_ID, $post_after, $post_before ) {
 	/**
 	 * Returns CPT arguments.
 	 *
-	 * @return array
+	 * @return array<string, mixed>
 	 */
-	public function getArgs() {
+	public function getArgs(): array {
 		$labels = array(
 			'name'                  => esc_html__( 'Bookings', 'commonsbooking' ),
 			'singular_name'         => esc_html__( 'Booking', 'commonsbooking' ),
@@ -598,10 +599,10 @@ public function getArgs() {
 	/**
 	 * Adds data to custom columns
 	 *
-	 * @param $column
-	 * @param $post_id
+	 * @param string $column
+	 * @param int $post_id
 	 */
-	public function setCustomColumnsData( $column, $post_id ) {
+	public function setCustomColumnsData( string $column, int $post_id ): void {
 		global $pagenow;
 
 		if ( $pagenow !== 'edit.php' || empty( esc_html( $_GET['post_type'] ) ) || esc_html( $_GET['post_type'] ) !== $this::$postType ) {
@@ -701,7 +702,7 @@ public function setCustomColumnSortOrder( \WP_Query $query ) {
 	/**
 	 * Registers metaboxes for cpt.
 	 */
-	public function registerMetabox() {
+	public function registerMetabox(): void {
 		// do not render the metabox if the user is on the login page (not yet logged in)
 		if ( ! is_user_logged_in() ) {
 			return;
@@ -722,9 +723,9 @@ public function registerMetabox() {
 	/**
 	 * Returns custom (meta) fields for Costum Post Type Timeframe.
 	 *
-	 * @return array
+	 * @return array<int, array<string, mixed>>
 	 */
-	protected function getCustomFields() {
+	protected function getCustomFields(): array {
 		// We need static types, because german month names dont't work for datepicker
 		$dateFormat = 'd/m/Y';
 		if ( str_starts_with( get_locale(), 'de_' ) ) {
@@ -910,9 +911,10 @@ public function displayBookingsAdminListNotice() {
 	/**
 	 * Displays a permanent admin-notice if booking overlaps
 	 *
+	 * @param \WP_Post $post
 	 * @return void
 	 */
-	public function displayOverlappingBookingNotice( $post ) {
+	public function displayOverlappingBookingNotice( \WP_Post $post ): void {
 
 		if ( get_transient( 'commonsbooking_booking_validation_failed_' . $post->ID ) ) {
 			echo commonsbooking_sanitizeHTML( get_transient( 'commonsbooking_booking_validation_failed_' . $post->ID ) );
@@ -923,11 +925,11 @@ public function displayOverlappingBookingNotice( $post ) {
 	 * Export user bookings using the supplied email. This is for integration with the WordPress personal data exporter.
 	 *
 	 * @param string $emailAddress
-	 * @param $page
+	 * @param int $page
 	 *
-	 * @return array
+	 * @return array<string, mixed>
 	 */
-	public static function exportUserBookingsByEmail( string $emailAddress, $page = 1 ): array {
+	public static function exportUserBookingsByEmail( string $emailAddress, int $page = 1 ): array {
 		$page         = intval( $page );
 		$itemsPerPage = 10;
 		$exportItems  = array();
@@ -1017,11 +1019,11 @@ public static function exportUserBookingsByEmail( string $emailAddress, $page =
 	 * Remove user bookings using the supplied email. This is for integration with the WordPress personal data eraser.
 	 *
 	 * @param string $emailAddress The email address
-	 * @param $page This parameter has no real use in this function, we just use it to stick to WordPress expected parameters.
+	 * @param int $page This parameter has no real use in this function, we just use it to stick to WordPress expected parameters.
 	 *
-	 * @return array
+	 * @return array<string, mixed>
 	 */
-	public static function removeUserBookingsByEmail( string $emailAddress, $page = 1 ): array {
+	public static function removeUserBookingsByEmail( string $emailAddress, int $page = 1 ): array {
 		// we reset the page to 1, because we are deleting our results as we go. Therefore, increasing the page number would skip some results.
 		$page         = 1;
 		$itemsPerPage = 10;
diff --git a/src/Wordpress/CustomPostType/CustomPostType.php b/src/Wordpress/CustomPostType/CustomPostType.php
index aa618461b..dfc8c8f14 100644
--- a/src/Wordpress/CustomPostType/CustomPostType.php
+++ b/src/Wordpress/CustomPostType/CustomPostType.php
@@ -34,7 +34,7 @@ abstract class CustomPostType {
 	protected $listColumns = null;
 
 	/**
-	 * @var array|null
+	 * @var array<int|string, string>|null
 	 */
 	protected $types = null;
 
@@ -69,13 +69,16 @@ public static function getWPNonceId(): string {
 	}
 
 	/**
-	 * @return array
+	 * @return array<string, mixed>
 	 */
-	protected static function getTaxonomyArgs() {
+	protected static function getTaxonomyArgs(): array {
 		throw new BadMethodCallException( 'Not implemented' );
 	}
 
-	public static function registerPostTypeTaxonomy() {
+	/**
+	 * @return void
+	 */
+	public static function registerPostTypeTaxonomy(): void {
 
 		$customPostType = static::getPostType();
 		$taxonomy       = static::getTaxonomyName();
@@ -99,11 +102,11 @@ public static function registerPostTypeTaxonomy() {
 	/**
 	 * Replaces WP_Posts by their title for options array.
 	 *
-	 * @param $data
+	 * @param mixed $data
 	 *
-	 * @return array
+	 * @return array<int|string, string>
 	 */
-	public static function sanitizeOptions( $data ) {
+	public static function sanitizeOptions( $data ): array {
 		$options = [];
 		if ( $data && is_array( $data ) ) {
 			foreach ( $data as $key => $item ) {
@@ -136,7 +139,7 @@ public static function sanitizeOptions( $data ) {
 	 *
 	 * @param mixed $type (item or location)
 	 *
-	 * @return array
+	 * @return array<int, array<string, mixed>>|null
 	 */
 	public static function getCMB2FieldsArrayFromCustomMetadata( $type ): ?array {
 
@@ -177,11 +180,12 @@ public static function getCMB2FieldsArrayFromCustomMetadata( $type ): ?array {
 	/**
 	 * Modifies Row Actions (like quick edit, trash etc) in CPT listings
 	 *
-	 * @param mixed $actions
+	 * @param array<string, string> $actions
+	 * @param \WP_Post $post
 	 *
-	 * @return mixed
+	 * @return array<string, string>
 	 */
-	public static function modifyRowActions( $actions, $post ) {
+	public static function modifyRowActions( array $actions, WP_Post $post ): array {
 
 		// remove quick edit for timeframes, restrictions and bookings
 		if ( $post->post_type == Timeframe::getPostType()
@@ -208,9 +212,9 @@ abstract public static function getView();
 	/**
 	 * Returns param for backend menu.
 	 *
-	 * @return array
+	 * @return array<int, mixed>
 	 */
-	public function getMenuParams() {
+	public function getMenuParams(): array {
 		return [
 			'cb-dashboard',
 			$this->getArgs()['labels']['name'],
@@ -230,11 +234,11 @@ abstract public function getArgs();
 	/**
 	 * Manages custom columns for list view.
 	 *
-	 * @param $columns
+	 * @param array<string, string> $columns
 	 *
-	 * @return mixed
+	 * @return array<string, string>
 	 */
-	public function setCustomColumns( $columns ) {
+	public function setCustomColumns( array $columns ): array {
 		if ( isset( $this->listColumns ) ) {
 			foreach ( $this->listColumns as $key => $label ) {
 				$columns[ $key ] = $label;
@@ -245,11 +249,11 @@ public function setCustomColumns( $columns ) {
 	}
 
 	/**
-	 * @param $columns
+	 * @param array<string, string> $columns
 	 *
-	 * @return mixed
+	 * @return array<string, string>
 	 */
-	public function setSortableColumns( $columns ) {
+	public function setSortableColumns( array $columns ): array {
 		if ( isset( $this->listColumns ) ) {
 			foreach ( $this->listColumns as $key => $label ) {
 				$columns[ $key ] = $key;
@@ -261,8 +265,10 @@ public function setSortableColumns( $columns ) {
 
 	/**
 	 * Removes title column from backend listing.
+	 *
+	 * @return void
 	 */
-	public function removeListTitleColumn() {
+	public function removeListTitleColumn(): void {
 		add_filter(
 			'manage_' . static::getPostType() . '_posts_columns',
 			function ( $columns ) {
@@ -275,8 +281,10 @@ function ( $columns ) {
 
 	/**
 	 * Removes date column from backend listing.
+	 *
+	 * @return void
 	 */
-	public function removeListDateColumn() {
+	public function removeListDateColumn(): void {
 		add_filter(
 			'manage_' . static::getPostType() . '_posts_columns',
 			function ( $columns ) {
@@ -290,13 +298,17 @@ function ( $columns ) {
 
 	/**
 	 * Initiates needed hooks.
+	 *
+	 * @return void
 	 */
-	abstract public function initHooks();
+	abstract public function initHooks(): void;
 
 	/**
 	 * Configures list-view
+	 *
+	 * @return void
 	 */
-	public function initListView() {
+	public function initListView(): void {
 		if ( array_key_exists( 'post_type', $_GET ) && static::$postType !== $_GET['post_type'] ) {
 			return;
 		}
@@ -345,10 +357,11 @@ function ( $args, $wp_query ) {
 	/**
 	 * Adds data to custom columns
 	 *
-	 * @param $column
-	 * @param $post_id
+	 * @param string $column
+	 * @param int $post_id
+	 * @return void
 	 */
-	public function setCustomColumnsData( $column, $post_id ) {
+	public function setCustomColumnsData( string $column, int $post_id ): void {
 
 		if ( $value = get_post_meta( $post_id, $column, true ) ) {
 			echo commonsbooking_sanitizeHTML( $value );
@@ -361,8 +374,10 @@ public function setCustomColumnsData( $column, $post_id ) {
 
 	/**
 	 * Adds Category filter to backend list view
+	 *
+	 * @return void
 	 */
-	public static function addAdminCategoryFilter() {
+	public static function addAdminCategoryFilter(): void {
 		$values = [];
 		$terms  = get_terms(
 			array(
@@ -370,7 +385,7 @@ public static function addAdminCategoryFilter() {
 			)
 		);
 		foreach ( $terms as $term ) {
-			$values[ $term->term_id ] = $term->name;
+			$values[ (string) $term->term_id ] = $term->name;
 		}
 		Filter::renderFilter(
 			static::$postType,
@@ -383,11 +398,11 @@ public static function addAdminCategoryFilter() {
 	/**
 	 * Checks if method has been called before in current request.
 	 *
-	 * @param $methodName
+	 * @param string $methodName
 	 *
 	 * @return bool
 	 */
-	protected function hasRunBefore( $methodName ): bool {
+	protected function hasRunBefore( string $methodName ): bool {
 		if ( array_key_exists( $methodName, $_REQUEST ) ) {
 			return true;
 		}
diff --git a/src/Wordpress/CustomPostType/Item.php b/src/Wordpress/CustomPostType/Item.php
index d29cb0eae..f7637d5f6 100644
--- a/src/Wordpress/CustomPostType/Item.php
+++ b/src/Wordpress/CustomPostType/Item.php
@@ -15,7 +15,7 @@ class Item extends CustomPostType {
 	/**
 	 * Initiates needed hooks.
 	 */
-	public function initHooks() {
+	public function initHooks(): void {
 		add_filter( 'the_content', array( $this, 'getTemplate' ) );
 		add_action( 'cmb2_admin_init', array( $this, 'registerMetabox' ) );
 
@@ -35,13 +35,13 @@ public function initHooks() {
 	/**
 	 * Handles the creation and editing of the terms in the taxonomy for the location post type
 	 *
-	 * @param $term_id
-	 * @param $tt_id
-	 * @param $taxonomy
+	 * @param int $term_id
+	 * @param int $tt_id
+	 * @param string $taxonomy
 	 *
 	 * @return void
 	 */
-	public static function termChange( $term_id, $tt_id, $taxonomy ) {
+	public static function termChange( int $term_id, int $tt_id, string $taxonomy ): void {
 		if ( $taxonomy == self::getTaxonomyName() ) {
 			// update all dynamic timeframes
 			Timeframe::updateAllTimeframes();
@@ -51,7 +51,7 @@ public static function termChange( $term_id, $tt_id, $taxonomy ) {
 	/**
 	 * Handles save-Request for items.
 	 */
-	public function savePost( $post_id, \WP_Post $post ) {
+	public function savePost( int $post_id, \WP_Post $post ): void {
 		if ( $post->post_type == self::$postType && $post_id ) {
 			// update all dynamic timeframes
 			Timeframe::updateAllTimeframes();
@@ -109,7 +109,7 @@ public static function getView() {
 	/**
 	 * Returns CPT args.
 	 *
-	 * @return array
+	 * @return array<string, mixed>
 	 */
 	public function getArgs(): array {
 		$labels = array(
@@ -312,14 +312,15 @@ public function registerMetabox() {
 		Settings::updateOption( 'commonsbooking_settings_metaboxfields', static::getPostType(), $metabox_fields );
 	}
 
-	public static function registerPostTypeTaxonomy() {
+	public static function registerPostTypeTaxonomy(): void {
 		parent::registerPostTypeTaxonomy();
 
 		// hook this for later, if we run it now, it would fail
 		add_action( 'cmb2_admin_init', array( self::class, 'registerTaxonomyMetaboxes' ) );
 	}
 
-	protected static function getTaxonomyArgs() {
+	/** @return array<string, mixed> */
+	protected static function getTaxonomyArgs(): array {
 		return array(
 			'label'             => esc_html__( 'Item Category', 'commonsbooking' ),
 			'rewrite'           => array( 'slug' => static::getPostType() . '-cat' ),
diff --git a/src/Wordpress/CustomPostType/Location.php b/src/Wordpress/CustomPostType/Location.php
index aecbded91..ba25948f4 100644
--- a/src/Wordpress/CustomPostType/Location.php
+++ b/src/Wordpress/CustomPostType/Location.php
@@ -13,7 +13,7 @@ class Location extends CustomPostType {
 	/**
 	 * Initiates needed hooks.
 	 */
-	public function initHooks() {
+	public function initHooks(): void {
 		add_filter( 'the_content', array( $this, 'getTemplate' ) );
 		add_action( 'cmb2_admin_init', array( $this, 'registerMetabox' ) );
 
@@ -30,7 +30,8 @@ public function initHooks() {
 		add_action( 'save_post', array( $this, 'savePost' ), 11, 2 );
 	}
 
-	protected static function getTaxonomyArgs() {
+	/** @return array<string, mixed> */
+	protected static function getTaxonomyArgs(): array {
 		return array(
 			'label'             => esc_html__( 'Location Category', 'commonsbooking' ),
 			'rewrite'           => array( 'slug' => self::getPostType() . '-cat' ),
@@ -43,7 +44,7 @@ protected static function getTaxonomyArgs() {
 	/**
 	 * Handles save-Request for location.
 	 */
-	public function savePost( $post_id, \WP_Post $post ) {
+	public function savePost( int $post_id, \WP_Post $post ): void {
 		if ( $post->post_type == self::$postType && $post_id ) {
 			$location = new \CommonsBooking\Model\Location( intval( $post_id ) );
 			$location->updateGeoLocation();
@@ -56,13 +57,13 @@ public function savePost( $post_id, \WP_Post $post ) {
 	/**
 	 * Handles the creation and editing of the terms in the taxonomy for the location post type
 	 *
-	 * @param $term_id
-	 * @param $tt_id
-	 * @param $taxonomy
+	 * @param int $term_id
+	 * @param int $tt_id
+	 * @param string $taxonomy
 	 *
 	 * @return void
 	 */
-	public static function termChange( $term_id, $tt_id, $taxonomy ) {
+	public static function termChange( int $term_id, int $tt_id, string $taxonomy ): void {
 		if ( $taxonomy == self::getTaxonomyName() ) {
 			// update all dynamic timeframes
 			Timeframe::updateAllTimeframes();
@@ -529,9 +530,9 @@ public function registerMetabox() {
 	 * Will get the metaboxes for the location settings that can also be overwritten by the global location settings.
 	 * We put them in a function here, so they can be retrieved by the OptionsArray.php as well.
 	 *
-	 * @return array[]
+	 * @return array<int, array<string, mixed>>
 	 */
-	public static function getOverbookingSettingsMetaboxes() {
+	public static function getOverbookingSettingsMetaboxes(): array {
 		return [
 			array(
 				'name' => esc_html__( 'Allow locked day overbooking', 'commonsbooking' ),
diff --git a/src/Wordpress/CustomPostType/Map.php b/src/Wordpress/CustomPostType/Map.php
index c1bb33f95..8679c8326 100644
--- a/src/Wordpress/CustomPostType/Map.php
+++ b/src/Wordpress/CustomPostType/Map.php
@@ -29,7 +29,7 @@ class Map extends CustomPostType {
 	/**
 	 * Initiates needed hooks.
 	 */
-	public function initHooks() {
+	public function initHooks(): void {
 		// Add shortcodes
 		add_shortcode( 'cb_map', array( MapShortcode::class, 'execute' ) );
 
diff --git a/src/Wordpress/CustomPostType/Restriction.php b/src/Wordpress/CustomPostType/Restriction.php
index 9996acd06..6c927a8e8 100644
--- a/src/Wordpress/CustomPostType/Restriction.php
+++ b/src/Wordpress/CustomPostType/Restriction.php
@@ -28,7 +28,7 @@ public static function getView() {
 	/**
 	 * Initiates needed hooks.
 	 */
-	public function initHooks() {
+	public function initHooks(): void {
 		// Add Meta Boxes
 		add_action( 'cmb2_admin_init', array( $this, 'registerMetabox' ) );
 		add_action( 'restrict_manage_posts', array( self::class, 'addAdminTypeFilter' ) );
@@ -73,7 +73,7 @@ public static function addAdminTypeFilter() {
 	/**
 	 * Adds filter dropdown // filter by item in restrictions List
 	 */
-	public static function addAdminItemFilter() {
+	public static function addAdminItemFilter(): void {
 		$items = \CommonsBooking\Repository\Item::get(
 			[
 				'post_status' => 'any',
@@ -100,7 +100,7 @@ public static function addAdminItemFilter() {
 	/**
 	 * Adds filter dropdown // filter by location in restrictions List
 	 */
-	public static function addAdminLocationFilter() {
+	public static function addAdminLocationFilter(): void {
 		$locations = \CommonsBooking\Repository\Location::get(
 			[
 				'post_status' => 'any',
@@ -127,7 +127,7 @@ public static function addAdminLocationFilter() {
 	/**
 	 * Adds filter dropdown // filter by status in restrictions list
 	 */
-	public static function addAdminStatusFilter() {
+	public static function addAdminStatusFilter(): void {
 		Filter::renderFilter(
 			static::$postType,
 			esc_html__( 'Filter By Status ', 'commonsbooking' ),
@@ -142,7 +142,7 @@ public static function addAdminStatusFilter() {
 	 * @param $column
 	 * @param $post_id
 	 */
-	public function setCustomColumnsData( $column, $post_id ) {
+	public function setCustomColumnsData( string $column, int $post_id ): void {
 
 		if ( $value = get_post_meta( $post_id, $column, true ) ) {
 			switch ( $column ) {
@@ -380,7 +380,7 @@ public function getArgs() {
 	/**
 	 * Registers metaboxes for cpt.
 	 */
-	public function registerMetabox() {
+	public function registerMetabox(): void {
 		$cmb = new_cmb2_box(
 			[
 				'id'           => static::getPostType() . '-custom-fields',
@@ -397,7 +397,7 @@ public function registerMetabox() {
 	/**
 	 * Returns custom (meta) fields for Costum Post Type Timeframe.
 	 *
-	 * @return array
+	 * @return array<int, array<string, mixed>>
 	 */
 	protected function getCustomFields(): array {
 		// We need static types, because german month names dont't work for datepicker
@@ -531,7 +531,7 @@ public static function getStates() {
 	/**
 	 * Handles save-Request for location.
 	 */
-	public function savePost( $post_id, $post ) {
+	public function savePost( int $post_id, \WP_Post $post ): void {
 		if ( $post->post_type == self::$postType && $post_id ) {
 			if ( $this->hasRunBefore( __METHOD__ ) ) {
 				return;
diff --git a/src/Wordpress/CustomPostType/Timeframe.php b/src/Wordpress/CustomPostType/Timeframe.php
index d20f8571f..37d31ea2b 100644
--- a/src/Wordpress/CustomPostType/Timeframe.php
+++ b/src/Wordpress/CustomPostType/Timeframe.php
@@ -86,7 +86,7 @@ class Timeframe extends CustomPostType {
 	 */
 	protected $menuPosition = 1;
 	/**
-	 * @var array
+	 * @var array<int|string, string>
 	 */
 	protected $types;
 
@@ -112,7 +112,7 @@ public function __construct() {
 	 *
 	 * @param bool $includeAll - When toggled, will include the "All" Option as a selection option
 	 *
-	 * @return array
+	 * @return array<int|string, string>
 	 */
 	public static function getTypes( bool $includeAll = false ): array {
 		$typeOptions = [];
@@ -135,7 +135,10 @@ public static function getTypes( bool $includeAll = false ): array {
 		return $typeOptions;
 	}
 
-	public static function getSimilarPostTypes() {
+	/**
+	 * @return string[]
+	 */
+	public static function getSimilarPostTypes(): array {
 		return [
 			self::$postType,
 			Booking::$postType,
@@ -145,14 +148,20 @@ public static function getSimilarPostTypes() {
 	/**
 	 * Callback function for booking code list.
 	 *
-	 * @param $field_args
-	 * @param $field
+	 * @param array<string, mixed> $field_args
+	 * @param \CMB2_Field $field
+	 * @return void
 	 */
-	public static function renderBookingCodeList( $field_args, $field ) {
+	public static function renderBookingCodeList( array $field_args, \CMB2_Field $field ): void {
 		\CommonsBooking\View\BookingCodes::renderTable( $field->object_id() );
 	}
 
-	public static function renderDateSelector( $field_args, $field ) {
+	/**
+	 * @param array<string, mixed> $field_args
+	 * @param \CMB2_Field $field
+	 * @return void
+	 */
+	public static function renderDateSelector( array $field_args, \CMB2_Field $field ): void {
 		?>
 		<label for="cmb2_multiselect_datepicker">
 			<?php echo commonsbooking_sanitizeHTML( __( 'Select Dates:', 'commonsbooking' ) ); ?>
@@ -246,8 +255,10 @@ public static function addAdminTypeFilter() {
 
 	/**
 	 * Adds filter dropdown // filter by item in timeframe List
+	 *
+	 * @return void
 	 */
-	public static function addAdminItemFilter() {
+	public static function addAdminItemFilter(): void {
 		$items = \CommonsBooking\Repository\Item::get(
 			[
 				'post_status' => 'any',
@@ -273,8 +284,10 @@ public static function addAdminItemFilter() {
 
 	/**
 	 * Adds filter dropdown // filter by location in timeframe List
+	 *
+	 * @return void
 	 */
-	public static function addAdminLocationFilter() {
+	public static function addAdminLocationFilter(): void {
 		$locations = \CommonsBooking\Repository\Location::get(
 			[
 				'post_status' => 'any',
@@ -300,8 +313,10 @@ public static function addAdminLocationFilter() {
 
 	/**
 	 * Adds filter dropdown // filter by location in booking list
+	 *
+	 * @return void
 	 */
-	public static function addAdminStatusFilter() {
+	public static function addAdminStatusFilter(): void {
 		$values = [];
 		foreach ( \CommonsBooking\Model\Booking::$bookingStates as $bookingState ) {
 			$values[ $bookingState ] = $bookingState;
@@ -316,8 +331,10 @@ public static function addAdminStatusFilter() {
 
 	/**
 	 * Adds filter dropdown // filter by location in timeframe List
+	 *
+	 * @return void
 	 */
-	public static function addAdminDateFilter() {
+	public static function addAdminDateFilter(): void {
 		$startDateInputName = 'admin_filter_startdate';
 		$endDateInputName   = 'admin_filter_enddate';
 
@@ -412,8 +429,10 @@ public static function filterAdminList( $query ) {
 
 	/**
 	 * Registers metaboxes for cpt.
+	 *
+	 * @return void
 	 */
-	public function registerMetabox() {
+	public function registerMetabox(): void {
 		$cmb = new_cmb2_box(
 			[
 				'id'           => static::getPostType() . '-custom-fields',
@@ -430,9 +449,9 @@ public function registerMetabox() {
 	/**
 	 * Returns custom (meta) fields for Costum Post Type Timeframe.
 	 *
-	 * @return array
+	 * @return array<int, array<string, mixed>>
 	 */
-	protected function getCustomFields() {
+	protected function getCustomFields(): array {
 		// We need static types, because german month names dont't work for datepicker
 		$dateFormat = 'd/m/Y';
 		if ( str_starts_with( get_locale(), 'de_' ) ) {
@@ -788,9 +807,9 @@ protected function getCustomFields() {
 	 * Get allowed timeframe types for selection box in timeframe editor
 	 * TODO: can be removed if type cleanup has been done (e.g. move BOOKIG_ID to Booking-Class and rename existing types )
 	 *
-	 * @return array
+	 * @return array<int|string, string>
 	 */
-	public static function getTypesforSelectField() {
+	public static function getTypesforSelectField(): array {
 		$types = self::getTypes();
 
 		// remove unused types
@@ -806,7 +825,7 @@ public static function getTypesforSelectField() {
 	/**
 	 * Returns style of item / location selection
 	 *
-	 * @return array
+	 * @return array<int, string>
 	 */
 	public static function getSelectionOptions(): array {
 		$selection = [ \CommonsBooking\Model\Timeframe::SELECTION_MANUAL_ID => esc_html__( 'Manual selection', 'commonsbooking' ) ];
@@ -820,9 +839,9 @@ public static function getSelectionOptions(): array {
 	/**
 	 * Returns grid options.
 	 *
-	 * @return array
+	 * @return array<int, string>
 	 */
-	public static function getGridOptions() {
+	public static function getGridOptions(): array {
 		return [
 			0 => esc_html__( 'Full slot', 'commonsbooking' ),
 			1 => esc_html__( 'Hourly', 'commonsbooking' ),
@@ -832,9 +851,9 @@ public static function getGridOptions() {
 	/**
 	 * Returns array with repetition options.
 	 *
-	 * @return array
+	 * @return array<string, string>
 	 */
-	public static function getTimeFrameRepetitions() {
+	public static function getTimeFrameRepetitions(): array {
 		return [
 			'norep' => esc_html__( 'No repetition', 'commonsbooking' ),
 			'manual' => esc_html__( 'Manual repetition', 'commonsbooking' ),
@@ -847,8 +866,12 @@ public static function getTimeFrameRepetitions() {
 
 	/**
 	 * Save the new Custom Fields values
+	 *
+	 * @param int $post_id
+	 * @param \WP_Post $post
+	 * @return void
 	 */
-	public function savePost( $post_id, WP_Post $post ) {
+	public function savePost( int $post_id, WP_Post $post ): void {
 		// This is just for timeframes
 		if ( $post->post_type !== static::getPostType() ) {
 			return;
@@ -906,7 +929,14 @@ public function savePost( $post_id, WP_Post $post ) {
 	}
 
 
-	public function updatedPostMeta( $meta_id, $object_id, $meta_key, $meta_value ) {
+	/**
+	 * @param int|string $meta_id
+	 * @param int $object_id
+	 * @param string $meta_key
+	 * @param mixed $meta_value
+	 * @return void
+	 */
+	public function updatedPostMeta( $meta_id, int $object_id, string $meta_key, $meta_value ): void {
 		// make sure, that action is only executed if timeframe is changed
 		if ( get_post( $object_id )->post_type !== self::getPostType() ) {
 			return;
@@ -941,7 +971,7 @@ public function updatedPostMeta( $meta_id, $object_id, $meta_key, $meta_value )
 	 *
 	 * @return void
 	 */
-	private static function sanitizeRepetitionEndDate( $postId ): void {
+	private static function sanitizeRepetitionEndDate( int $postId ): void {
 		$repetitionEnd = get_post_meta( $postId, \CommonsBooking\Model\Timeframe::REPETITION_END, true );
 		if ( $repetitionEnd ) {
 			$repetitionEnd = strtotime( '+23 Hours +59 Minutes +59 Seconds', $repetitionEnd );
@@ -1016,7 +1046,11 @@ public static function updateAllTimeframes() {
 	 *
 	 * @return void
 	 */
-	public static function manageTimeframeMeta( $post_id ) {
+	/**
+	 * @param int $post_id
+	 * @return void
+	 */
+	public static function manageTimeframeMeta( int $post_id ): void {
 		$postModel = get_post( $post_id );
 		// This is just for timeframes
 		if ( $postModel->post_type !== static::getPostType() ) {
@@ -1143,9 +1177,9 @@ public static function removeIrrelevantPostmeta( \CommonsBooking\Model\Timeframe
 	/**
 	 * Returns CPT arguments.
 	 *
-	 * @return array
+	 * @return array<string, mixed>
 	 */
-	public function getArgs() {
+	public function getArgs(): array {
 		$labels = array(
 			'name'                  => esc_html__( 'Timeframes', 'commonsbooking' ),
 			'singular_name'         => esc_html__( 'Timeframe', 'commonsbooking' ),
@@ -1225,10 +1259,11 @@ public function getArgs() {
 	/**
 	 * Adds data to custom columns
 	 *
-	 * @param $column
-	 * @param $post_id
+	 * @param string $column
+	 * @param int $post_id
+	 * @return void
 	 */
-	public function setCustomColumnsData( $column, $post_id ) {
+	public function setCustomColumnsData( string $column, int $post_id ): void {
 
 		// we alter the  author column data and link the username to the user profile
 		if ( $column == 'timeframe-author' ) {
diff --git a/src/Wordpress/Options/OptionsTab.php b/src/Wordpress/Options/OptionsTab.php
index 7b556a443..92f22837e 100644
--- a/src/Wordpress/Options/OptionsTab.php
+++ b/src/Wordpress/Options/OptionsTab.php
@@ -12,11 +12,13 @@
  */
 class OptionsTab {
 
-	public $option_key = COMMONSBOOKING_PLUGIN_SLUG . '_options';
-	public $id;
-	public $tab_title;
-	public $content;
-	public $groups;
+	public string $option_key = COMMONSBOOKING_PLUGIN_SLUG . '_options';
+	public string $id;
+	public string $tab_title;
+	/** @var array<string, mixed> */
+	public array $content;
+	/** @var array<string, mixed> */
+	public array $groups;
 
 	// Error type for backend error output
 	public const ERROR_TYPE = 'commonsbooking-options-error';
@@ -27,6 +29,7 @@ class OptionsTab {
 	 */
 	private $metabox;
 
+	/** @param array<string, mixed> $content */
 	public function __construct( string $id, array $content ) {
 		$this->id        = $id;
 		$this->content   = $content;
@@ -38,7 +41,7 @@ public function __construct( string $id, array $content ) {
 		add_action( 'cmb2_save_options-page_fields', array( self::class, 'savePostOptions' ), 10 );
 	}
 
-	public function register() {
+	public function register(): void {
 		$this->registerOptionsTab();
 		$this->registerOptionsGroups();
 	}
@@ -46,7 +49,7 @@ public function register() {
 	/**
 	 * Register Tab
 	 */
-	public function registerOptionsTab() {
+	public function registerOptionsTab(): void {
 
 		$default_args = array(
 			'id'           => $this->id,
@@ -76,7 +79,7 @@ public function registerOptionsTab() {
 	/**
 	 * Register Tab Contents (Groups + Fields)
 	 */
-	public function registerOptionsGroups() {
+	public function registerOptionsGroups(): void {
 
 		foreach ( $this->groups as $group ) {
 			$group = static::prependTitle( $group ); /* prepend title + description html */
@@ -93,9 +96,9 @@ public function registerOptionsGroups() {
 	/**
 	 * If array contains title or description, create a new row containing this text
 	 *
-	 * @param array $metabox_group
+	 * @param array<string, mixed> $metabox_group
 	 *
-	 * @return array $metabox_group with title + description added as row
+	 * @return array<string, mixed> $metabox_group with title + description added as row
 	 */
 	public static function prependTitle( array $metabox_group ): array {